Polycrystalline silicon substrate having a thermally-treated surface, and process of making the same

ABSTRACT

A substrate for liquid jet recording head including an electrothermal converting body comprising a heat generating resistor capable of generating thermal energy and a pair of wirings electrically connected to said heat generating resistor, characterized in that said substrate includes a base member constituted by a polycrystalline material and said polycrystalline base member has a thermal oxide layer formed by subjecting the surface of said polycrystalline base member to thermal oxidation treatment and thermally softening treatment. A process for producing said substrate, a liquid jet recording head in which said substrate is used, and a liquid jet recording apparatus in which said substrate is used. By using the above specific substrate, there can be provided a desirable elongated recording head which is free of a warpage or a curved portion at a reduced production cost.

FIELD OF THE INVENTION

The present invention relates to a polycrystalline silicon-basedsubstrate for use in a liquid jet recording head of conducting recordingby discharging a liquid recording medium through discharging outletsutilizing thermal energy, and a process for producing said substrate.The present invention also relates to a liquid jet recording head inwhich said substrate is used and a liquid jet recording apparatus inwhich said substrate is used.

BACKGROUND OF THE INVENTION

There is known a liquid jet recording method for conducting recording bydischarging a liquid recording medium such as ink through dischargingoutlets utilizing thermal energy to sputter said liquid recording mediumwhereby said liquid recording medium is deposited on a recording membersuch as papers, plastic sheets, fabrics, or the like. The liquid jetrecording method is of a so-called non-impact recording method, and ithas various advantages in that the noise at the recording can be reducedto a negligible order, there is not a particular restriction for therecording member used, and color recording can be relatively easilyattained. And as for the apparatus, that is, the liquid jet recordingapparatus, for practicing the above liquid jet recording method, thereare advantages in that the structure thereof can be relativelysimplified, liquid discharging nozzles can be arranged at a highdensity, and a high speed recording can be relatively easily attained.In view of this, the liquid jet recording method has recently receivedhe public attention, and various studies have been made thereon.Incidentally, a number of liquid jet recording apparatus have been puton the market.

Shown in FIG. 5(A) is a schematic cross-eyed view illustrating theprincipal part of an example of a recording head used in such liquid jetrecording apparatus. FIG. 5(B) is a schematic cross-sectional view takenalong the liquid pathway and at the face perpendicular to the substrateof the recording head shown in FIG. 5(A).

As apparent from FIG. 5(A) and FIG. 5(B), the recording head is providedwith a substrate 8 for liquid jet recording head comprising a pluralityof discharging outlets 7 each serving to discharge a liquid recordingmedium such as ink, liquid pathways 6 each corresponding one of thedischarging outlets 7, a liquid chamber 10 serving to supply a liquidrecording medium to each of the liquid pathways, heat generatingresistors 2a each serving to supply thermal energy to the liquidrecording medium, and wirings 3a, 3b for applying an electric signal tothe heat generating resistors 2a.

The substrate for liquid jet recording head 8 is of the configurationshown in FIG. 5(B) wherein a heat generating resistor layer 2 isdisposed on a base member 1, a wiring layer 3 constituted by a materialhaving a good electroconductivity is laminated on said heat generatingresistor layer 2, and a portion 2a of the heat generation resistor layerwhere the wiring layer 3 is not disposed functions as a heat generatingresistor.

In this configuration, when an electric signal is applied to the heatgenerating resistor 2a through the wirings 3a, 3b the heat generatingresistor 2a is energized. The substrate for liquid jet recording head 8may be provided with a protective layer 4 for the purpose of protectingthe wirings 3a, 3b and the heat generating resistor 2a. The protectivelayer 4 serves to prevent occurrence of electric corrosion or/andelectric breakdown at the heat generating resistor 2a and the wirings3a, 3b.

As the base member 1 of the substrate for liquid jet recording head 8,there can be mentioned plate-like members of silicon, glass, ceramics,or the like. However, in general, a single crystal silicon plate is usedas the base member. The reason for this is due to the followingsituation. That is, in the case where a glass plate is used as the basemember 1, there are disadvantages in that the glass plate is poor inthermal conductivity, and when the energization frequency (the drivepulse in other words) for the heat generating resistor 2a is increased,there is a fear that the heat generated by the heat generating resistorbecomes excessively accumulated within the base member 1 and as aresult, ink in the liquid jet recording head is heated by virtue of theheat accumulated to cause bubbles, resulting in providing defects in theink discharging performance.

In the case where a ceramic plate is used as the base member 1, thereare advantages such that the size of the substrate can be enlarged to acertain extent, and a ceramic plate having a larger thermal conductivitythan that of the glass plate can be selectively used. However, even inthe case of using such a ceramic plate, there are disadvantages suchthat the ceramic plate is usually accompanied by surface defects such aspinholes or minute protrusions of some microns to some tens microns insize because it is produced by baking powdery raw materials, and suchsurface defects are liable to short-circuit or disconnect the wirings,wherein a desirable production yield is hardly attained. There arefurther disadvantages in this case such that the ceramic plate isusually of a surface roughness of Ra (center line mean roughness)=about0.15 μm, and because of this, it is difficult to provide a surfaceroughness optimum for forming a desirable heat generating resistor layer2 excelling in durability thereon; specifically in the case of preparinga liquid jet recording head using a plate made of alumina ceramics,because of the above reasons, a removal is often occurred between thebase member 1 and the heat generating resistor layer 2 or a cavitationis often occurred at a part of the heat generating resistor layer formedon the defective surface of the base member when the bubbles generatedare extinguished, resulting in disconnecting the heat generatingresistor layer, wherein the performance of the heat generating resistorlayer is eventually deteriorated.

In order to eliminate these problems in the case of using the ceramicbase member 1, there is a proposal of polishing such roughened surfaceof the ceramic base member to smooth said surface whereby improving theadhesion between the base member 1 and the heat generating resistorlayer 2 and preventing occurrence of the premature disconnection of theheat generating resistor layer which will be cased because ofcavitations centralized at a part of the heat generating resistor layer.However, this proposal is poor in practicability since the aluminaceramics are of a high hardness and because of this, their surfaceroughness is hardly adjusted as desired.

Other than this proposal, there is another proposal in order toeliminate the above problems in that a glaze layer (a welded glassycomponent layer) is formed on the surface of such ceramic base member tothereby provide an alumina glaze base member. However, it is almostimpossible to form the glaze layer at a thickness of less than a valueof 40 to 50 μm by the manner employable in the formation of a glazelayer. As well as in the case of using the glass base member, problemsrelating to occurrence of excessive accumulation of heat are liable tooccur also in this case. Therefore, this proposal is also poor inpracticability.

In the case of using a single crystal silicon plate as the base member1, the above described problems relating to occurrence of excessiveaccumulation of heat are not occurred and the single crystal siliconwafer excels in surface property, and because of this, the foregoingproblems relating to disconnection of the wirings and the like are notoccurred. For this, for example, Japanese Unexamined Patent PublicationNo. 125741/1990 describes a substrate for the foregoing liquid jetrecording head utilizing thermal energy, in which a single crystalsilicon wafer is used.

Incidentally, in recent years, in the field of recording using theliquid jet recording method, there has been an increased societal demandfor early provision of a recording apparatus capable of obtaining a highquality record image at an improved speed. In order to enable to conductrecording on a wide recording member in reply to such societal demandfor high speed recording, various studies have been made of alarge-sized recording head, i.e., a so-called full-line recording headhaving a widened discharging width corresponding to a large-sizedrecording member.

The results of the studies have revealed that the use a single crystalsilicon wafer is optimum as the base member as long as the recordinghead to be prepared is of a relatively small size, but the use of asingle crystal silicon wafer in the case of obtaining a large-sizedrecording head entails such problems as will be described below. Becauseof this, there are subjects necessary to be solved in order for thesingle crystal silicon wafer to be usable in a substrate for thelarge-sized recording head.

That is, in the case where a substrate for liquid jet recording head isprepared using a base member comprising a single crystal siliconmaterial, the single crystal base member, i.e., a single crystal siliconwafer is usually obtained by quarrying a single crystal silicon ingotproduced by the pull method. The single crystal ingot which can bepresently produced by the pull method is a rod-like shaped one of 8inches in diameter and about 1 m in length at the maximum. Therefore,there is eventually a limit for the size of a single crystal siliconwafer which can be quarried from the single crystal ingot. However, itis possible to quarry a single crystal silicon wafer having an enlargedsize from the single crystal ingot. In this case, problems are, however,entailed in that the utilization efficiency is greatly reduced,resulting in unavoidably raising the cost of the resulting singlecrystal wafer, and this leads to raising the production cost of a finalproduct.

In the substrate for liquid jet recording head, in order to facilitatethermal energy to transmit to the liquid recording medium, there isusually disposed, on the surface of the base member, a heat accumulatinglayer (a lower layer in other words) capable of attaining a desirablebalance between the heat accumulating property and the heat radiatingproperty. In this case, the substrate is obtained in a manner that asingle crystal silicon wafer is obtained by quarrying the abovedescribed single crystal ingot, the surface of the single crystalsilicon wafer obtained is subjected to thermal oxidation to form a SiO₂layer as the heat accumulating layer, the foregoing heat generatingresistor layer and the foregoing wirings are successively formed, andthe resultant is cut into a plurality of pieces each capable of servingas a substrate for liquid jet recording head.

In the viewpoint of obtaining a large-sized recording head, the presentinventor examined these members obtained in the above manner. As aresult, there was obtained a finding that some of them, which werequarried from the opposite end portions of the single crystal siliconwafer, are deformed in such a bow-shaped form as shown in FIG. 9(A). Andtheir deformed magnitude (which will be hereinafter called "warpmagnitude" or "warp degree") was found to be ranging in the range of 60to 90 μm. As for these deformed members, it was found that they are aptto break when their deformation is forcibly corrected. And as for someof the base members which are slight in deformation, it was found thatthere are still problems such that uniform polishing is sometimes hardlyattained in the successive polishing step after the quarrying step,precise pattering sometimes cannot be conducted in the step ofpatterning wirings on the base member, and sometimes, it is difficult toprecisely electrically connect the wirings arranged on the base memberto an IC or the like.

It was also found that in the case where a liquid jet recording headshould be obtained using such deformed base member, the liquid jetrecording head unavoidably causes a positional deviation of a liquidrecording medium to a recording member on which recording is to beperformed due to the distortion of the base member, resulting inproviding defects such as missing dots or/and uneven dots for an imagerecorded.

It is a matter of course that in the case where the end portions of thesingle crystal silicon wafer which are apt to cause the foregoingdeformation are not used as a base member for a substrate for liquid jetrecording head, the production cost for the substrate for liquid jetrecording head unavoidably becomes very expensive.

The present inventor made studies of the reason why such work in processfor a substrate for liquid jet recording head is deformed as abovedescribed. As a result, it was found that in the case of the work inprocess for a substrate for liquid jet recording head not having theforegoing thermal oxide layer as the heat accumulating layer on the basemember, such deformation is hardly occurred, and thus, the occurrence ofsuch deformation is due to the thermal oxidation process upon formingthe foregoing heat accumulating layer. And there were obtained findingsthat since after the single crystal silicon wafer having been subjectedto thermal oxidization, it is cooled wherein the end portions of thesingle crystal silicon wafer, particularly four corners thereof, arecooled for the first time, tensile stresses are caused at the peripheryin a state as expressed by arrow marks in FIG. 8(A) and those stressesthen become distributed into the inside in a state as expressed by (+)marks in FIG. 8(B); that when this single crystal silicon wafer is cutin order to obtain a substrate for liquid jet recording head, part ofthose stresses is released to make the substrate deformed in such astate as above described; and that when a film for the heat generatingresistor and a film for the wirings are successively formed on suchsingle crystal silicon base member, the resulting work in processbecomes accompanied by a warpage for which desirable patterning cannotbe performed because the focusing position upon exposure is deviated.

On the basis of the above findings, it was found that there is aninherent limit for the single crystal silicon wafer to be used as thebase member for a substrate for liquid jet recording head in order toattain elongation of the substrate. Therefore, in order to obtain anelongated liquid jet recording head capable of attaining high speedrecording, it is necessary to integrate a plurality of relatively shortsubstrates for recording head. However, it is extremely difficult toadjust each of the joint portions among such substrates so that nonegative influence is provided for an image recorded.

Thus, it is an earnest desire to provide an inexpensive substrate forliquid jet recording head which can be effectively produced withouthaving any restriction for its form depending upon the productionprocess and without occurrence of problems relating to deformation andthe like and which enables to easily attain high speed recording.

SUMMARY OF THE INVENTION

The principal object of the present invention is to solve the foregoingproblems of the conventional substrate for liquid jet recording head andto provide an elongated substrate comprising a specific material forliquid jet recording head which enables to obtain a large-seizedrecording head.

Another object of the present invention is to provide an elongatedsubstrate for liquid jet recording head in which an elongated basemember composed of a polycrystalline silicon material is used.

A further object of the present invention is to provide a large-seizedliquid jet recording head which can be effectively produced withoutintegrating a plurality of substrates as in the case of using a singlecrystal silicon wafer and without the foregoing problems relating to theoccurrence of a deformation in the work in process for a substrate forliquid jet recording head and the occurrence of a reduction in qualityof an image recorded due to said deformation, and the occurrence ofdefective exposure due to the warpage in the work in process for asubstrate for liquid jet recording head, which are found in the case ofusing a single crystal silicon wafer.

A further object of the present invention is to provide a liquid jetrecording apparatus provided with the above liquid jet recording headwhich enables to attain high speed recording of providing a high qualityrecorded image.

A further object of the present invention is to provide a process forproducing a substrate for liquid jet recording head, which includes thestep of forming a thermal oxide layer having a good surface property onthe surface of a base member comprising a polycrystalline siliconmaterial which is used in the above-described substrate for liquid jetrecording head.

In order to solve the foregoing problems of the conventional substratefor liquid jet recording head and in order to attain the above objects,The present inventor made studies through experiments which will belater described. As a result, the present inventor obtained thefollowing findings. That is, in the case of using a polycrystallinesilicon material as the base member for a substrate for liquid jetrecording head, (i) the foregoing problems in the case of using a singlecrystal silicon wafer which are related to the restriction for the sizeof a substrate for liquid jet recording head and to the occurrence ofdeformation of the substrate can be effectively solved, and a liquid jetrecording head capable of providing a high quality recorded image at ahigh speed can be effectively produced at a reduced production cost; and(ii) in the case of forming a thermal oxide layer on the polycrystallinesilicon base member, when the thermal oxide layer is firstly formed byway of thermal oxidation and the thermal oxide layer is followed bysubjecting to thermally softening treatment at a temperature region atwhich the thermal oxide layer is softened, the thermal oxide laterbecomes to have a smooth and continuous surface with no surface stepwherein a thermal oxide layer having an excellent surface property isprovided.

The present invention has been accomplished based on the findingsobtained through the experiments by the present inventor.

The present invention includes a substrate for liquid jet recording headof the configuration which will be described below, a liquid jetrecording head in which said substrate is used, a liquid jet recordingapparatus in which said substrate is used, and a process for producingsaid substrate.

The present invention provides a substrate for liquid jet recording headincluding an electrothermal converting body comprising a heat generatingresistor capable of generating thermal energy and a pair of wiringselectrically connected to said heat generating resistor, wherein saidsubstrate includes a base member composed of a polycrystalline siliconmaterial.

The substrate for liquid jet recording head according to the presentinvention have various advantages in that even if the substrate is of agreatly prolonged length, it can be effectively produced at a lowerproduction cost in comparison with the foregoing case wherein a singlecrystal silicon wafer is used; no deformation is occurred not only inthe case where the substrate is in the form of a normal shape but alsoin the case where the substrate is in the form of an elongated shape;and highly precise wire-patterning can be easily attained.

The present invention provides a liquid jet recording head including: aliquid discharging outlet; a substrate for liquid jet recording headincluding an electrothermal converting body comprising a heat generatingresistor capable of generating thermal energy for discharging liquidfrom said discharging outlet and a pair of wirings electricallyconnected to said heat generating resistor, said pair of wirings beingcapable of supplying an electric signal for generating said thermalenergy to said heat generating resistor; and a liquid supplying pathwaydisposed in the vicinity of said electrothermal converting body of saidsubstrate, wherein said substrate includes a base member composed of apolycrystalline silicon material.

The liquid jet recording head according to the present invention ismarkedly advantageous in that a desired elongation therefor can beeasily attained. Particularly, the elongation of a liquid jet recordinghead in the case of using a single crystal silicon wafer can be attainedfor the first time by integrating a plurality of substrates for liquidjet recording head. However, in the present invention, such integrationprocess is not necessary to be carried out.

Thus, the elongated liquid jet recording head according to the presentinvention is free of the problems relating to occurrence of unevennessas for images recorded which are caused due to the integration of aplurality of substrates for liquid jet recording head in the case of anelongated liquid jet recording head in which a single crystal siliconwafer is used. Other than this advantage, the liquid jet recording headaccording to the present invention has further advantages. That is,since the substrate excels in surface property and the head work inprocess is free of warpage, the liquid jet recording head can beproduced at a high yield, and since the positional precision for aliquid recording medium discharged from the discharging outlets to bedeposited on a recording member is always insured, there is stably andcontinuously provided a high quality recorded image.

The present invention provides a liquid jet recording apparatuscomprising: a liquid jet recording head including a liquid dischargingoutlet; a substrate for liquid jet recording head including anelectrothermal converting body comprising a heat generating resistorcapable of generating thermal energy for discharging liquid from saiddischarging outlet and a pair of wirings electrically connected to saidheat generating resistor, said pair of wirings being capable ofsupplying an electric signal for generating said thermal energy to saidheat generating resistor; a liquid supplying pathway disposed in thevicinity of said electrothermal converting body of said substrate; andan electric signal supplying means capable of supplying an electricsignal to said heat generating resistor of said recording head, whereinsaid substrate includes a base member composed of a polycrystallinesilicon material.

The liquid jet recording head apparatus according to the presentinvention enables to conduct high speed recording wherein a high qualityrecorded image is stably and repeatedly provided.

The present invention provides a process for producing a substrate forliquid jet recording head in which an electrothermal converting bodycomprising a heat generating resistor and a pair of wirings electricallyconnected to said heat generating resistor is disposed on an oxide layeras the heat accumulating layer formed on a base member, said process ischaracterized by including the step of forming a thermal oxide layer(which will be hereinafter referred to as thermal oxide layer, SiO₂ filmor SiO₂ layer according to the situation) having a smoothly flat surfaceas said heat accumulating layer on the surface of said polycrystallinesilicon member. The step of forming the thermal oxide layer in theprocess for producing a substrate for liquid jet recording headaccording to the present invention is conducted in a manner which willbe described in the following (i) or (ii). That is, the manner (i) isthat a given polycrystalline silicon base member is provided, thesurface of the polycrystalline silicon base member is subjected tothermal oxidation treatment to form a thermal oxide layer (that is, aSiO₂ layer), and the thermal oxide layer is subjected to thermallysoftening treatment to thereby form a thermal oxide layer having asmoothly flat surface (that is, a heat accumulating layer) on thepolycrystalline silicon base member. The manner (ii) is that a givenpolycrystalline silicon base member is provided, and the surface of thepolycrystalline silicon base member is subjected to thermal oxidationtreatment and thermally softening treatment substantially at the sametime to thereby form a thermal oxide layer having a smoothly flatsurface (that is, a heat accumulating layer) on the polycrystallinesilicon base member.

According to the process for producing a substrate for liquid jetrecording head of the present invention, although a polycrystallinesilicon material inherently having an irregular surface is used as thebase member, a desirable thermal oxide layer while providing anexcellent surface flatness for the layer formed. Thus, it is possible toform, on a polycrystalline silicon base member, a heat accumulatinglayer which is equivalent to the foregoling heat accumulating layerformed on a single crystal silicon base member. The heat accumulatinglayer thus formed has a smoothly flat surface and excels in durability,and because of this, wirings and the like can be formed on the heataccumulating layer in a desirable state in that problems relating tooccurrence of a breakdown or the like are hardly occurred therefor.

BRRIEF DECRIPTION OF THE DRAWINGS

FIG. 1(A) is a schematic plan view illustrating the principal part of anexample of a substrate for a liquid jet recording head arding to thepresent invention.

FIG. 1(B) is a schematic cross-sectional view, taken along lin X-Y inFIG. 1(A).

FIG. 2 is a schematic cross-sectional view illustrating an example of abase member for a substrate for a liquid jet recording head according tothe present invention.

FIG. 3 is a schematic cross-sectional view for explaining themanufacturing process of producing a liquid jet recording head in thepresent invention.

FIGS. 4(A) through 4(C) are schematic explanatory views showing thesteps of forming a thermal oxide layer on the surface of apolycrystalline silicon base member in the present invention.

FIG. 5(A) is a schematic exploded perspective view illustrating theprincipal parts of an example of a liquid jet recording head suable foruse with this invention.

FIG. 5(B) is a schematic cross-sectional view taken along the liquidpathway and at the face perpendicular to the substrate of the ding headshown in FIG. 5(B).

FIG. 6 is a schematic view illustrating an embodiment of a known type ofrecording apparatus which can be provided with a liquid jet recordinghead prepared using the present invention.

FIG. 7 is a schematic explanatory view of an example of a thermaloxidation apparatus used for thermally oxidizing the surface of a basemember for a substrate for a liquid jet recording head in tresentinvention.

FIGS. 8(A) and 8(B) are schematic views for explaining the mechanism ofcausing a bowed portion at as base member.

FIGS. 9(A) through 9(C) are schematic views for depicting the formationof a bowed portion at the time of cutting a base member.

FIG. 9(D) is a schematic view of the manner of measuring the magnitudeof a bowed portion present in a base member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Experiments

In the field of solar cell, a plate-like polycrystalline member has beenused. However, in the case of using such polycrystalline silicon memberin a substrate for liquid jet recording head, it is required to have aflat surface in a desirable state for the reason that precise wiringsand the like are disposed thereon. However, The polycrystalline siliconmember, being different from a single crystal member, contains variouscrystals with a different orientation, and because of this, it has anirregular surface. In view of this, it is a common recognition in thefield of liquid jet recording head that a desirable flatness which isrequired for the base member for a substrate for liquid jet recordinghead is hardly attained for the surface of the polycrystalline siliconmember even by means of the polishing technique capable of providing amirror-ground surface. Hence, a polycrystalline silicon member has nevertried to use as the base member in the field of liquid jet recordinghead.

Disregarding this common recognition, the present inventor tried to usea polycrystalline silicon material as the base member for a substratefor liquid jet recording head as described in the following experiments.As described in the following, based on the findings obtained in theexperiments, there was obtained a finding that a polycrystalline siliconmaterial can be effectively used as the base member for a substrate forliquid jet recording head.

Description will be made of the experiments conducted by the presentinventor.

Experiment A

In the case of producing a semiconductor device using a conventionalsingle crystal wafer, the mechanochemical polishing technique isemployed in order to minimize work defect zones present on the singlecrystal wafer. In the mechanochemical polishing technique, an abrasivematerial comprising a colloidal silica added with various alkalies suchas NaOH, KOH, organic amines, and the like is used in the primarypolishing, and an abrasive material comprising a colloidal silica addedwith ammonia is used in the secondary polishing.

However, when the surface of a polycrystalline silicon member isprocessed by the above polishing technique, steps are usually occurredat the surface. The present inventor presumed that this occurrence wouldbe caused due to the difference in the amount of the silicon material tobe etched by the alkali component of the abrasive material dependingupon the crystal orientation.

The following experiment was conducted based on this presumption.

Firstly, there were prepared a plurality of single crystal base membersamples in the following manner. That is, a single crystal silicon ingot(8 inch×110 cm) of a boron dopant p-type was prepared by pulverizing ahigh purity polycrystal rod with a residual impurity content of lessthan 1 ppb obtained by way of the precipitation reaction throughhydrogen reduction and pyrolysis of SiHCl₃, fusing the resultant, andpulling the fused material toward the (111) direction by a conventionalCZ method. The single crystal ingot obtained was then formed into aprismatic shape by means of a grinder. The resultant was quarried bymeans of a multi-wire saw, to thereby obtain a plurality of platemembers. Each of the plate members obtained was subjected to lappingtreatment to remove an about 30 μm thick surface portion wherebyobtaining a plate member with a flat surface.

Separately, there were prepared a plurality of polycrystalline siliconbase member samples in the following manner. That is, there was provideda high purity polycrystalline silicon material, obtained in accordancewith the same precipitation reaction through hydrogen reduction andpyrolysis as in the above case of obtaining the foregoing single crystalsilicon material. The material obtained was then pulverized, theresultant was fused in a quartz crucible at 1420° C., the fused materialwas poured into a casting mold made of graphite, followed by cooling,whereby an ingot of 40 cm in square size was obtained. The ingotobtained was quarried by means of a multi-wire saw to thereby obtain aplurality of plate members. Each of the plate members obtained wassubjected to lapping treatment to remove an about 30 μm thick surfaceportion whereby obtaining a plate member having a flat surface.

In this way, as for each of the single crystal material and thepolycrystalline silicon material, there were obtained a plurality ofsamples each having a size of 300 (mm)×150 (mm)×1.1 (mm) (for thesimplification purpose, this will be abbreviated as "300×150×1.1 (mm)")as shown in Table 1.

In the following, there was used a single side polishing machine,produced by Speedfarm Kabushiki Kaisha, in the polishing processing.

For each sample, the primary polishing and the secondary polishing wereseparately conducted under the below-described respective conditions.The surface finishing efficiency in relation to the presence or absenceof alkali upon the polishing was evaluated. The evaluated resultsobtained are collectively shown in Table 1.

The conditions in the primary polishing: abrasive fabric:polyurethane-impregnated polyester non-woven fabric; abrasive material:colloidal silica (0.06 um in particle size); polishing pressure: 250g/cm² ; polishing temperature: 42° C.; processing speed: 0.7 um/min.

The conditions in the secondary polishing: abrasive fabric: suede typeurethane foam; abrasive material: silica fine powder (0.01 um inparticle size); polishing pressure: 175 g/cm² ; polishing temperature:32° C.; processing speed: 0.2 um/min.

From the results shown in Table 1, it was found that even in the case ofa polycrystalline silicon base member, it is possible to attain asurface flatness similar to that obtained in the case of a singlecrystal silicon member by omitting the addition of alkali upon thepolishing, and a polycrystalline silicon member can be used as the basemember for a substrate for liquid jet recording head.

Experiment B

In this experiment, discussion was made of a difference between themagnitude of a single crystal silicon base member to be deformed andthat of a polycrystalline silicon base member to be deformed.

The single crystal silicon base member sample was prepared in thefollowing manner. That is, a single crystal ingot (8 inch×110 cm) of aboron dopant p-type was prepared by pulverizing a high puritypolycrystal rod with a residual impurity content of less than 1 ppbobtained by way of the precipitation reaction through hydrogen reductionand pyrolysis of SiHCl₃, fusing the resultant, and pulling the fusedmaterial toward the (111) direction by a conventional CZ method. Thesingle crystal ingot was formed into a prismatic shape by means of agrinder. The resultant was quarried by means of a multi-wire saw toobtain a plate member. The plate member obtained was subjected tolapping treatment to remove an about 30 um thick surface portion wherebyobtaining a plate member having a flat surface. The end portions of theresultant were chanferred by means of a beveling machine, followed byfinishing by way of the polish processing, to thereby obtain amirror-ground member with a surface roughness of Rmax 150 Å.

Then, the surface of the mirror-ground member was subjected to thermaloxidation by way of the pyrogenic oxidation method (the hydrogen burningoxidation method) shown in FIG. 7. The thermal oxidation in this case isconducted, for example, in the following manner. That is, hydrogen gasand oxygen gas are separately introduced into a quartz tube 73, whereinthese gases are reacted with each other to produce H₂ O, and theunreacted residuals are burned. The mirror-ground member as an object 71to be treated is arranged in the quartz tube 73, and the object isheated to a desired temperature by an electric furnace 74.

The thermal oxidation of the surface of the mirror-ground member usingthe oxidation apparatus was conducted under the conditions of 1 atm forthe gas pressure, 1150° C. for the treating temperature, and 14 hoursfor the treating period of time, while introducing hydrogen gas andoxygen gas into the quartz tube, whereby a 3 μm thick thermal oxidelayer was formed on said member.

In this way, there were prepared six single crystal silicon base membersamples each having a different size as shown in Table 2.

Separately, there were prepared a plurality of polycrystalline siliconbase member samples in the following manner. That is, there was firstlyprovided a high purity polycrystalline silicon material, obtained inaccordance with the same precipitation reaction through hydrogenreduction and pyrolysis as in the above case of obtaining the foregoingsingle crystal silicon material. The material obtained was thenpulverized, the resultant was fused in a quartz crucible at 1420° C.,the fused material was poured into a casting mold made of graphite,followed by cooling, whereby an ingot of 120 cm in square size wasobtained. In this case, the higher the cooling speed is, the smaller thecrystal grain size is, and because of this, the crystal grain size inthe vicinity of the center becomes greater. In view of this, the portionof the ingot obtained having a mean grain size of 2 mm was quarried bymeans of a multi-wire saw to obtain a polycrystalline silicon platemember. The plate member obtained was subjected to lapping treatment toremove an about 30 μm thick surface portion whereby obtaining a platemember having a flat surface. The end portions of the resultant werechanferred by means of a beveling machine, followed by finishing by wayof the polish processing, to thereby obtain a mirror-ground member witha surface roughness of Rmax 150 Å.

Then, the surface of the mirror-ground member was subjected to thermaloxidation by way of the above described pyrogenic oxidation method underthe same conditions employed in the above case, whereby a 3 um thickthermal oxide layer was formed on said member.

In this way, there were prepared six polycrystalline silicon base membersamples each having a different size as shown in Table 2.

As for each of the resultant single crystal silicon base member samplesand the resultant polycrystalline base member samples, on the surfacethereof, there were laminated an aluminum layer (4500 Å thick) as thewirings, a HfB₂ layer (1500 Å thick) as the heat generating resistor, aTi later (50 Å) as the layer serving to improve the contact with theprotective layer to be formed above, a SiO₂ layer (1.5 μm thick) as theprotective layer, a Ta layer (5000 Å thick), and a polyimide film (3 μmthick). Thus, there were obtained six substrates for liquid jetrecording head in each case.

Now, in the production of a liquid jet recording head using a substratefor liquid jet recording head, an about 20 μm thick negative dry film isformed on the substrate, followed by subjecting to exposure for thepurpose of patterning liquid pathways. In this patterning process, ifthe substrate is accompanied by a warp, the focusing position is oftendeviated to cause a defective exposure.

In this viewpoint, as for each substrate, the magnitude of the warp wasevaluated. The evaluation of the warp was conducted by placing thesample on a measuring table and measuring its maximum displacementmagnitude by means of a dial gauge of 1 μm in minimum scale.

The results obtained are collectively shown in Table 2. The values shownin Table 2 are values relative to the maximum warp magnitude of thepolycrystalline silicon substrate sample of 300×150×1.1 (mm) in size,which was set at 1.

Based on the results shown in Table 2, the followings are understood.That is, the respective warp magnitudes of the polycrystalline siliconsubstrate samples examined are slight and substantially the same, but asfor the warp magnitude of each of the single crystal silicon substratesamples examined, it starts increasing from the single crystal siliconsubstrate sample of 500×150×1.1 (mm) in size, and the single crystalsilicon substrate sample of 800×150×1.1 (mm) in size is great as much as3 in terms of relative value; in the case of the single crystal siliconsubstrate sample of 2 in warp magnitude relative value, the focusingposition in the exposure process is liable to deviate to cause adefective exposure, and in the case of the single crystal siliconsubstrate sample of 3 in warp magnitude relative value, the focusingposition in the exposure process is definitely deviated to cause adefective exposure; and the single crystal silicon substrate sample of500×150×1.1 (mm) in size is the usable limit for producing a liquid jetrecording head.

Experiment C

In this experiment, as for each of a single crystal silicon base memberand a polycrystalline silicon base member, studies were made of theinterrelation between the crystal grain size and the occurrence of adeformation at the base member due to warpage.

There were prepared 10 mirror-ground single crystal silicon base membersamples each having a size of 300×150×1.1 (mm) (Sample No. 1) in thesame manner as in Experiment B.

Separately, there were prepared a plurality of mirror-groundpolycrystalline silicon base members each having a size of 300×150×1.1(mm) in the same manner as in Experiment B. Incidentally, thepolycrystalline silicon ingot obtained is of a varied crystal grain sizewhich is gradually increased from the casting mold side toward thecenter. In view of this, appropriate portions of the polycrystallinesilicon ingot were selected upon the quarrying, to thereby obtain sevenpolycrystalline silicon plates (Sample Nos. 2 to 8) each having adifferent mean crystal grain size as shown in the columns Sample No. 2to Sample No. 8 of Table 3. As for each of these seven plates, therewere obtained 10 base member samples. In this case, the mean crystalgrain size was measured by a crystal grain size measuring method basedon the cutting method described in the description of the ferritecrystal grain size examining method in the JIS G 0552.

As for each of the single crystal silicon base member sample (SampleNo. 1) and the polycrystalline silicon base member samples, a 3 μm thickthermal oxide layer was formed in accordance with the pyrogenicoxidation method described in Experiment B.

Now, an elongated integral liquid jet recording head is obtained bycutting the substrate for liquid jet recording head into a plurality ofstrip forms each being dedicated for a head. In this case, there is aproblem in that only the heads cut from the opposite sides of thesubstrate are always bow-shaped. The situation wherein these bow-shapedheads are caused is shown in FIG. 9(A).

Incidentally, if the face to be polished is warped upon conducting thepolishing processing, a problem is entailed in that since the distancebetween the heat generating resistor and the discharging outlet face isnot uniform, a defect is liable to provide for an image recorded. Inview of this, for the purpose of examining the process yield in thepolishing process, each of the opposite side portions of the base membersample was cut by means of a slicer to thereby obtain two strip-shapedtest samples of 10 mm in width. Thus, there were obtained 20 testsamples as for each of the samples described in Table 3.

As for each sample, the maximum deformation magnitude was measured byplacing it on a precision XY-table. The measuring manner in this case isshown in FIGS. 9(B) to 9(D). In the manner shown in FIG. 9(D), themeasurement of the maximum deformation magnitude was conducted bysetting the points a and b to the X axis of the XY-table and measuring adeformation magnitude in the Y direction.

As for the results obtained, the sample which was beyond a givenallowable deformation magnitude in the polishing process was made to beunfitness, and the fitness proportion was obtained as for each sample.The evaluated results are collectively shown in Table 3, in which thevalues shown are values relative to the fitness proportion of Sample No.8 of 0.001 mm in mean crystal grain size, which was set at 1.

Based on the results shown in Table 3, there was obtained a finding thatin general, a polycrystalline silicon base member is superior to asingle crystal silicon base member in terms of deformation magnitude dueto warpage. Particularly, as for the polycrystalline silicon base membersamples of a mean crystal grain size exceeding 8 um, their superiorityto the single crystal silicon base member is not significant; as for thepolycrystalline silicon base member samples of a mean crystal grain sizein the range of 2 um to 8 um, their superiority to the single crystalsilicon base member is significant, but they are inferior to thepolycrystalline silicon base member samples of a mean crystal grain sizeof 2 um or less. From this situation, it is understood that in order forthe polycrystalline silicon member base member to be effectively usable,it is desired to be preferably of a mean crystal grain size of 8 μm orless, more preferably of a mean crystal grain size of 2 μm or less.

Experiment D

As for the base member for a substrate for liquid jet recording head,since wirings are disposed thereon, it is required to have a flatsurface in a desirable state. Therefore, even in the case where apolycrystalline silicon material is used as the base member, it isrequired to meet this requirement.

By the way, it is known to use a polycrystalline silicon material as asubstrate in the field of solar cell. In this case, as for the surfacestate of the polycrystalline silicon substrate, there is not such aseverer requirement with regard to surface flatness as in the case ofthe base member for a substrate for liquid jet recording head. In fact,polycrystalline silicon substrates used in the field of solar cellusually contain certain contaminants. A polycrystalline silicon ingotused for obtaining a polycrystalline silicon substrate for a solar cellis prepared by fusing a silicon material in a quartz crucible andcooling the fused silicon material to solidify. The fused siliconmaterial in this case is very chemically reactive and it unavoidablychemically reacts with the constituent quartz of the crucible in a wayexpressed by the chemical formula SiO₂ +Si→2SiO. As a result, uponcooling and solidifying the fused silicon material, the silicon isfirmly adhered to the inner wall face of the crucible. An when a straindue to the difference between the coefficient of thermal expansion ofthe silicon material and that of the quartz is provided therein, a crackis liable to occur at the crucible. In order that the ingot formed canbe easily taken out from the crucible, a powdery release agent is coatedto the inner wall face of the crucible. Therefore, such release agent isunavoidably contaminated into the ingot. The presence of suchcontaminant in the ingot is not problematic in the case of the substratefor a solar cell. However, in the case of disposing wirings on thesurface of a polycrystalline member obtained in accordance with thismanner, when the surface of the polycrystalline silicon member issubjected to polishing treatment in order to provide a mirror-groundsurface, the contaminants present in the polycrystalline silicon membercause defects at the resulting mirror-ground surface wherein thecontaminants are remained at said surface while providing pits or/andprotrusions of some tens microns in size. The presence of such defectsentails a problem in that when the wirings are patterned by means of aphotolithography technique, there are often occurred portions for whicha resist is hardly applied or other portions where a resist isaccumulated, resulting in causing disconnection, shortcircuit or thelike for the wirings. Further, in the case where such defects arepresent at the position where a heat Generating resistor is arranged,there is a fear that cavitation damages are centralized to cause earlydisconnection for the wirings at the time when bubbles are Generated fordischarging ink.

In this experiment, in view of this situation, studies were made of theinfluence of a contaminant contained in a polycrystalline material uponusing the polycrystalline silicon material as the base member for asubstrate for liquid jet recording head.

Firstly, from a single crystal silicon material obtained in accordancewith the manner described in Experiment B, a single crystal plate of330×150×1.1 (mm) in size was quarried, and it was subjected to lappingtreatment and polishing treatment, to thereby obtain a mirror-groundsingle crystal silicon base member having a surface with a surfaceroughness of Rmax 150 Å. This base member was made to be Sample No. 1.

At this stage, the surface state of this base member (Sample No. 1) wasobserved using a binary image processing by CCD line sensor system(trademark name: SCANTEC, produced by NaGase Sangyo Kabushiki Kaisha).As a result, it was found that the number of defects per unit area isless than 1/cm² at every measured point in the detectable range with adiameter of more than 1 um, since no release agent was used in thiscase. The observed result is shown in Table 4.

Separately, a polycrystalline silicon material was fused in a quartzcrucible with no application of a release agent to the inner wall faceof said quartz crucible, and a polycrystalline silicon ingot of 50 cm insquare size was obtained. From this ingot, there was quarried apolycrystalline silicon plate of the same size as the above singlecrystal silicon plate, and it was subjected to lapping treatment andpolishing treatment, to thereby obtain a mirror-ground polycrystallinesilicon base member having a surface with a surface roughness of Rmax150 Å. This base member was made to be Sample No. 2.

The surface state of this base member was observed in the same manner asin the case of the above single crystal silicon base member. As aresult, it was found that the number of defects per unit area is lessthan 1/cm² at every measured point in the detectable range with adiameter of more than 1 μm, since no release agent was used in thiscase. The observed result is shown in Table 4.

Then, there were prepared a plurality of base members (Sample Nos. 3 to6) in the same manner as in the case of preparing Sample No. 2, exceptfor using a release agent. The amount of the release agent used was madedifferent in each case. As for each of the resultant base members(Sample Nos. 3 to 6), the surface state was observed in the same manneras in the case of the above single crystal silicon member (Sample No.1). As a result it was found that the base members of Sample Nos. 3 to 6are respectively of less than 5/cm² less than 10/cm² less than 50/cm²,and less than 100/cm² in terms of the number of defects.

Then, as for each of the above base members (Sample Nos. 1 to 6), thesurface thereof was subjected to thermal oxidation treatment in the samemanner as in Experiment B, to thereby form a 3 μm thick thermal oxidelayer.

In order to examine the situation of causing disconnection orshortcircuit due to the foregoing contaminant, on the thermal oxidelayer of each sample a return wiring pattern of 20 μm in line width and10 μm in line interval as a test wiring pattern was arranged by way offorming a 4500 Å thick Al film by a conventional magnetron sputteringtechnique. In this case, considering the wiring pattern of a liquid jetrecording head, as for the return wirings for each sample, there wasemployed a pattern of 8 mm for the wiring length and 4736 for the numberof the wirings. And this pattern was made as a test pattern as for eachsample. 15 this patterns were arranged in each sample.

Then, as for each sample, continuity check was conducted by connecting aprobe-pin to each wiring terminal. The evaluation of the continuitycheck was conducted based on the criteria in which the case whereneither disconnection nor shortcircuit is present is made to be fitness.The evaluated result was expressed by the number of the patterns withneither disconnection nor shortcircuit among the 15 patterns,specifically, the number of the patterns having been judged as beingfitness/the 15 patterns. The results obtained are collectively shown inTable 4.

Based on the results shown in Table 4, the following findings wereobtained. That is, (i) the process yield in the case of apolycrystalline silicon member with no release agent is substantiallythe same as that in the case of a single crystal silicon base member;(ii) the process yield in the case of a polycrystalline silicon memberwith a release agent and which is of 5/cm² or less in therms of thenumber of defects of more than 1 μm in diameter is substantially thesame as that in the case of a single crystal silicon base member; (iii)the process yield in the case of a polycrystalline silicon member with arelease agent and which is of 10/cm² or less in therms of the number ofdefects of more than 1 μm in diameter is slightly inferior to that inthe case of a polycrystalline silicon member with a release agent andwhich is of 5/cm² or less in therms of the number of defects of morethan 1 um in diameter; and (iv) the process yield in the case of apolycrystalline silicon member with a release agent and which is of50/cm² or less in therms of the number of defects of more than 1 μm indiameter is markedly inferior, and such polycrystal silicon base memberis practically unacceptable. In addition, the polycrystalline siliconmember with a release agent and which is of 100/cm² or less in therms ofthe number of defects of more than 1 μm in diameter is practicallyunacceptable also. Based on these findings, there was obtained thefollowing knowledge. That is, in order for a polycrystalline siliconmaterial to be usable as the base member for a substrate for liquid jetrecording head, it is required to have a surface with a surface flatness(a surface smooth state) preferably of 10/cm² or less, more preferablyof 5/cm² in therms of the number of defects of more than 1 μm indiameter.

Experiment E

In this experiment, studies were made in the viewpoint of eliminatingthe occurrence of surface steps at the surface of a polycrystallinesilicon member in the case of using said polycrystalline silicon memberas the base member for a substrate for liquid jet recording head.

As previously described, in the case of using a single crystal siliconmaterial as the base member for a substrate for liquid jet recordinghead, a heat accumulating layer is usually formed on the surface of thesingle crystal silicon base member for the purpose of attaining adesirable balance between the heat radiating property and the heataccumulating property so that the resulting liquid jet recording headexhibits good characteristics. As the heat accumulating layer in thiscase, there is usually employed a SiO₂ layer formed by thermallyoxidizing the surface of the single crystal silicon base member.

In this experiment, using a polycrystalline silicon member instead ofthe above single crystal silicon base member, a SiO₂ layer as the heataccumulating layer was formed by thermally oxidizing the surface of thepolycrystalline silicon member, and the surface state of the resultantSiO₂ layer was examined. As a result, it was found that steps of somethousands angstroms in terms of maximum degree are present among thecrystal grains at the surface of the SiO₂ layer.

In the case where such steps are present at the surface of the basemember for a substrate for liquid jet recording head, damages are forcedto centralize in the vicinity of such step by virtue of a thermal shockcaused upon the heating and cooling operations or/and a cavitationcaused upon discharging a recording liquid. And if the heat generatingresistor having being formed on such step, a problem entails in that thereliability is reduced particularly in terms of durability. Especially,in the case where recording liquid discharging is repeated at a highspeed, the cavitation is centralized in the vicinity of such step and asa result, a rupture is occurred at the heat generating resistor at arelatively earlier stage. As a mean in order to solve these problems,there is considered a manner of forming the above SiO₂ layer andflattening the surface of the SiO₂ layer by the polishing technique.But, the above problems cannot be satisfactorily solved by this manner.That is, the SiO₂ layer, which is accompanied by such surface steps ofsome thousands angstroms as above described, is desired to be of athickness of some microns, and therefore, it is difficult to desirablysolve the above problems without hindering the function of the SiO₂layer. In order to solve the above problems, there is considered anothermanner of making the SiO₂ layer thickened to a remarkable extent andpolishing the surface thereof to a certain extent. However, this manneris practically unacceptable also, since the SiO₂ layer having anexcessive thickness does not function as the heat accumulating layer,and in addition, the formation of such excessively thick SiO₂ layer isnot economical.

Independently, the formation of the heat accumulating layer (that is,the SiO₂ layer) was conducted by means of each of sputtering,thermal-induced CVD, plasma CVD, and ion beam evaporation techniques. Inany case, there were found problems such that the film thickness isuneven, the film-forming period is relatively long, or foreign mattersgenerated during the film formation are contaminated into a film toresult in providing protrusions having a size of some microns indiameter, which will eventually become causes of causing the foregoingrupture by virtue of a cavitation. It was also found that suchprotrusion occurred permits an electric current to leak therethrough,resultin_(G) in causing a shortcircuit. Based on these findings, therewas obtained a knowledge that any of the above-mentioned vacuumfilm-forming methods is not suitable for the formation of the foregoingheat accumulating layer (that is, the SiO₂ layer).

Then, the formation of the heat accumulating layer (that is, the SiO₂layer) was formed by means of each of the spin-on-glass method and thedipping method. As a result, it was found that any of the SiO₂ filmsformed by these methods is poor in film quality, any of these methods isdifficult to attain a desired film quality, contamination of foreignparticles into a film formed is often occurred in any of these methods,and therefore, any of these methods is not suitable for the formation ofthe foregoing heat accumulating layer.

By the way, in the case of producing a semiconductor device, there isusually employed the so-called flattening process as a means ofeliminating the problem relating to the occurrence of a breakdown at astep portion of a multi-layered wiring. As a typical example of theflattening process, there can be mentioned a PSG film-reflowingtechnique which is often employed in the case of preparing a MOSLSI. Toflatten steps of a PSG film as the interlayer insulating film by thistechnique is conducted, for example, in a manner that a few mole % of P₂O₅ is incorporated into a SiO₂ film formed, for example, by means of theCVD technique to thereby reduce the softening point of the PSG film,followed by subjecting to thermal treatment (reflow treatment). Thereflow temperature in this case is made to be in the range of about 800°to 1000° C. with a due care about occurrence of a negative influence tothe wirings and the like formed.

However, the above flattening process is not effective to eliminate theforegoing surface steps at the thermal oxide layer formed on thepolycrystalline silicon base member for a substrate for liquid jetrecording head. That is, in the case of a liquid jet recording headwhich is apparently different from the semiconductor device in theviewpoints of constitution, function, performance and use purpose, thesubstrate of the liquid jet recording head is required to besufficiently durable against a temperature of about 1100° C. since theheat generating resistor disposed on said substrate is energized to saidtemperature for generating thermal energy for discharging liquidrecording medium upon conducting recording using the liquid jetrecording head. The constituent material of the substrate is, therefore,is essential to meet this requirement.

Now, in the case where a base member constituting the above substrate iscomposed of a polycrystalline silicon material which is apparentlydifferent from the PSG film used in the semiconductor device and athermal oxide layer is formed on the polycrystalline silicon base memberby way of thermal oxidation treatment, a step is unavoidably occurred atthe surface of the thermal oxide layer as above described. The presentinventor employed the above-described step-eliminating method in thesemiconductor device in order to eliminate this step, but the objectcould not be accomplished. This situation is apparent with reference tothe results obtained through the following experiments. That is, insummary, the problem relating to the step at the surface of the thermaloxide layer could not be eliminated even by conducting the reflowtreatment using about 1100° C., which is beyond the maximum reflowtreatment temperature of about 1000° C. employed upon the stepelimination in the semiconductor device.

Thus, it was found that any conventional technique is not effective ineliminating the problem relating to occurrence of a step (a surface stepin other words) at the thermal oxide layer formed on the polycrystallinesilicon base member for a substrate for liquid jet recording head.

In view of this, the present inventor made a trial of eliminating theproblem relating to the occurrence of a surface step at the thermaloxide layer by employing a so-called thermally softening treatmentthrough the following experiments. In the experiments, there wereemployed two manners; a manner (i) in which a thermal oxide layer isformed on a polycrystalline silicon base member by thermally oxidizingthe surface of the polycrystalline silicon base member, and the thermaloxide layer is subjected to thermally softening treatment; and a manner(ii) in which the thermal oxidation treatment and thermally softeningtreatment are concurrently conducted for the surface of apolycrystalline silicon base member.

In the followinG, with reference to FIG. 4(A) to FIG. 4(C), descriptionwill be made of (a) the reason why a thermal oxide layer (a SiO₂ layer)formed on a polycrystalline silicon base member by thermally oxidizingthe surface of the polycrystalline silicon base member becomes to have asurface step at the surface thereof and also of (b) a finding obtainedby the present inventor through the experiments in that a SiO₂ layerfree of a surface step can be formed on a polycrystalline silicon basemember in the case where a thermal oxide layer with a surface stepformed on the polycrystalline silicon base member by thermally oxidizingthe surface of the polycrystalline silicon base member is subjected tothermally softening treatment at a temperature at which the thermaloxide layer is softened.

That is, when a polycrystalline base member 11 as such shown in FIG.4(A) itself is thermally oxidized, its volume is increased uponconducting the thermal oxidation and the constituent crystal grains 12are individually oxidized at a different oxidation speed because thesecrystal grains are different one from the other in terms of crystalorientation, and because of this, as shown in FIG. 4(B), the thicknessof the resulting thermal oxide film 13 becomes different depending oneach of the crystal grains 12, resulting in causing steps at thesurface. The line a in FIG. 4(B) indicates the surface position of thepolycrystalline silicon base member 11 prior to the thermal oxidation.Particularly, for instance, when an about 3 μm thick thermal oxide film13 (that is, a SiO₂ layer) is formed on the surface of thepolycrystalline silicon base member 11, steps caused at the surface ofthe thermal oxide film are of about 1000 Å. In the case of a liquid jetrecording head prepared using a substrate for liquid jet recording headcomprising a polycrystalline silicon base member having a thermal oxidelayer with such surface steps formed thereon, cavitation damages causedwhen bubbles are extinguished above the heat generating resistor of thesubstrate are centralized at step portions upon conducting recordingwhile driving the liquid jet recording head, resulting in making theheat generating resistor damaged at very early stage.

Herein, description will be made of the thermal oxidation process of thesurface of a polycrystalline silicon base member. At the very beginningstage of the forming of the thermal oxide layer by thermally oxidizingthe surface of the polycrystalline silicon base member, a linearrelationship is established between the thickness of the thermal oxidefilm 13 and the oxidation speed. That is, the reaction of oxygen gas(O₂) at the interface between the polycrystalline silicon (Si) and thesilicon oxide (SiO₂) constituting the thermal oxide layer becomes arate-limiting factor. In this case, the oxidation speed of the oxygengas is different depending on the crystal orientation. On the otherhand, after the thermal oxide layer 13 having been formed to a certainextent, the process of the oxygen gas to be diffused in this thermaloxide layer 13 becomes a rate-limiting factor. It is considered that thediffusing speed of the oxygen gas in the thermal oxide layer 13 is notgoverned by the crystal orientation of the silicon crystal grain 12. Inthis connection, it is presumed that a surface step at the surface ofthe thermal oxide layer 13 (that is, the thermal oxide film) formed asfor each of the crystal grains 12 of the polycrystalline silicon basemember 11 will be occurred at the very beginning stage of the thermaloxidation process and after the formation of the thermal oxide layer 13having proceeded to a certain extent, the steps are not grown further.

When heat treatment (that is, thermally softening treatment) isconducted for said steps at an elevated temperature (a softeningtemperature) at which the polycrystalline material is not fused, thethermal oxide layer gradually becomes showing a flowability, eventuallyresulting in providing a smoothly flat surface as shown in FIG. 4(C).Particularly, to apply thermal energy makes the surface state of thethermal oxide layer deformed and flattened such that the surface stepsare averaged, and this leads to prevent occurrence of the problem ofcentralizing cavitation damages at the heat generating resistor formedon the thermal oxide layer, resulting in providing an improvement in thedurability of the heat generating resistor.

Being different from the case of forming a multi-layered wiring in theprocess of producing a LSI wherein the interlayer insulating film on thewiring is flattened, the present invention is aimed at flattening thesurface steps of the thermal oxide layer formed on the polycrystallinesilicon base member, and therefore, the purpose can be attained byproviding a certain flowability for the steps.

The above thermally softening treatment can be conducted after thethermal oxidation treatment (the formation of the thermal oxide layer)or it can be conducted concurrently together with the thermal oxidationtreatment. In any case, the polycrystalline silicon base member may beincorporated with a given impurity and the polycrystalline siliconmember. In this case, the softening temperature of the thermal oxidelayer is lowered and as a result, an improvement is provided for thetreating efficiency. Particularly, the thermally softening treatment canbe conducted at a relatively low temperature and the period of time forthe thermally softening treatment can be shortened. However, in the casewhere the thermally softening treatment is conducted at a relativelyhigh temperature, the softening of the thermal oxide layer effectivelyproceeds and as a result, the flattening of the steps can be moreeffectively conducted.

By proceeding the softening state of the thermal oxide layer in thisway, an improvement can be attained for the close contact between thethermal oxide later formed on the polycrystalline silicon base memberand a heat generating resistor formed on the thermal oxide layer.

In order to confirm the effects provided by conducting the thermallysoftening treatment, the following experiments were conducted bypreparing a substrate for liquid jet recording head.

Experiment E-1

In this experiment, studies were made of the effects of apolycrystalline silicon base member having a thermal oxide layer formedby conducting the foregoing thermally softening treatment following thethermal oxidation treatment by preparing a substrate for liquid jetrecording head using said base member.

Firstly, a polycrystalline silicon ingot with a mean crystal grain sizeof about 2 mm was produced by the foregoing casting technique. Theresultant ingot was quarried to obtain five rectangular plates. Each ofthe plates obtained was subjected to lapping treatment and polishingtreatment, to thereby obtain a polycrystalline silicon base member of300×150×1.1 (mm) in size and having a mirror-ground surface with asurface roughness of Rmax 150 Å.

On the surface of each of the polycrystalline silicon base members,there was formed a thermal oxide layer by thermally oxidizing saidsurface in the manner and under the same conditions employed inExperiment B, except in that the quartz tube (see, 73 in FIG. 7) wasreplaced by a quartz tube made of SiC. Each of the resultant fivepolycrystalline silicon base members each having a thermal oxide layerthereon was introduced into a thermal oxidation furnace, wherein thethermal oxide layer was subjected to thermally softening treatment in anatmosphere maintained at a different temperature of 1380° C., 1330° C.,1280° C., 1230° C. or 1180° C. for an hour. Thus, there were obtainedfive polycrystalline silicon base member samples as Sample Nos. 1 to 5.

As a result of having conducted the above thermally softening treatment,each of the polycrystalline silicon base members became to have a heataccumulating layer comprising the thermal oxide layer (that is, the SiO₂layer) thereon. The thickness of the heat accumulating layer (that is,the SiO₂ layer) in each case was found to be 3.0 μm.

As for the heat accumulating layer of each polycrystalline silicon basemember sample, evaluation was made of its surface step state whilemeasuring it by means of a conventional surface profiler by stylus. Theconditions for the measurement and the criteria for the evaluation weremade as follows.

The measurement conditions:

the stylus scanning distance: 10 mm,

the number of the positions measured: 15 positions as for each sample,and

the position measured: 15 intersections of the three linear lines bywhich the short side of 150 mm in width is divided into four equal zonesand the five linear lines by which the long side of 300 mm in length isdivided into six equal zones as for each sample.

The evaluation criteria:

⊚: the case where the maximum step height among the 15 measuredpositions is between 0 μm and less than 0.05 μm,

∘: the case where the maximum step height among the 15 measuredpositions is between 0.05 μm and less than 0.1 μm, and

X: the case where the maximum step height among the 15 measuredpositions is more than 0.1 μm.

The evaluated results revealed that the surface step state of each ofSample Nos. 1 and 2 is ⊚, the surface step state of each of Sample Nos.3 and 4 is ∘, and the surface step state of Sample No. 5 is X.

As for each of the polycrystalline silicon base member samples obtainedin the above, on the surface of the heat accumulating layer, there wereformed a plurality of heat generating resistor each comprising HfB₂(size: 20 μm×100 μm, thickness: 0.16 μm, wiring density: 16 Pel (thatis, 16/mm)) and a plurality of Al electrodes (width: 20 μm, thickness:0.6 μm) each being connected to one of the heat generating resistorsusing the photolithography technique. Then, a protective layercomprising SiO₂ /Ta was formed above each portion where the heatgenerating resistor and electrode were formed by means of a conventionalsputtering technique. Thus, there was obtained five substrates forliquid jet recording head each being of the configuration shown in FIGS.1(A) and 1(B).

In the above, Sample No. 1 was found to be accompanied by a deformationwhich was caused at the time of the thermally softening treatmentwherein an excessively high softening temperature was employed. And inthe process of preparing a substrate for liquid jet recording head usingthis sample, a crack was occurred at the base member, and because ofthis, a substrate for liquid jet recording head could not be prepared.

As for each of the resultant four substrates for liquid jet recordinghead of Sample Nos. 2 to 5, a plurality of liquid pathways and a liquidchamber were formed using a dry film followed by cutting with the use ofa slicer to form a plurality of discharging outlets, whereby a liquidjet recording head of the configuration shown FIGS. 5(A) and 5(B) wasobtained.

As for each of the resultant four liquid jet recording heads thedischarging durability test was conducted by repeatedly applying 1.1 Vth(Vth: discharging threshold voltage) and a driving pulse (a printingsignal) with a pulse width of 10 μs to each of the heat generatingresistors to thereby discharge ink from each of the discharging outlets.

The evaluation of the durability of each of the liquid jet recordingheads was conducted by obtaining a survival rate of the heat generatingresistors, specifically the number of the heat generating resistors notdisconnected versus the total number of the heat generating resistors,when the integrated value of the driving pulses became each of 1×10⁷,1×10⁸ and 3×10⁸. The evaluated results are shown in each of the columnsof Sample Nos. 2 to 4 of Table 5-1.

From the evaluated results it is understood that in the case of each ofthe four recording heads based on Sample Nos. 2 to 4, no cavitationdisconnection is occurred and the survival rate is 100% even after 3×10⁸times repetition of the driving pulse, but in the case of the recordinghead based on Sample No. 5, a cavitation disconnection is occurred at anearly stage, and the survival rate is markedly low. Based on thesefacts, it was recognized that by forming a thermal oxide layer on thesurface of a polycrystalline silicon base member by thermally oxidizingthe surface of the polycrystalline silicon base member and subjectingthe thermal oxide layer to thermally softening treatment at atemperature in the range of 1230° C. to 1330° C., there can be formed adesirable heat accumulating layer with a desirable surface wherein stepsare smoothed in a desirable state, and there can be obtained a desirableliquid jet recording head which provides superior results in thedischarging durability test.

Experiment E-2

In this experiment, studies were made of the effects of apolycrystalline silicon base member having a thermal oxide layer (a heataccumulating layer) formed by concurrently conducting the foregoingthermal oxidation treatment and thermally softening treatment.

Following the manner employed in Experiment E-1, there were obtainedfive polycrystalline silicon base member samples (Sample Nos. 6 to 10)each being of 300×150×1.1 (mm) in size and having a mirror-groundsurface with a surface roughness of Rmax 150 Å.

On the surface of each of the polycrystalline silicon base members,using the same apparatus used in Experiment E-1, there was formed athermal oxide layer by concurrently conducting the thermally oxidationtreatment and thermally softening treatment for the surface of thepolycrystalline silicon base member. Particularly, each of the fivepolycrystalline silicon base member samples was introduced into athermal oxidation furnace, oxygen gas was supplied therein by way of thepyrogenic technique, and the inside of the thermal oxidation furnace wasmaintained a given temperature, whereby the surface of thepolycrystalline silicon base member sample was thermally oxidized andthermally softened at the same time, resulting in forming a heataccumulating layer (a thermal oxide layer, that is, a SiO₂ layer) on thepolycrystalline silicon base member sample. The inside of the thermaloxidation furnace was maintained at a different temperature of 1380° C.,1330° C., 1280° C., 1230° C. or 1180° C. in each case. In order to makethe thickness of the heat accumulating layer (the thermal oxide layer orthe SiO₂ layer) to be 3 μm in each case, the heat treatment period wasmade to be 5 hours, 7 hours, 8 hours, 11 hours, or 14 hours. Thus, therewere obtained five polycrystalline silicon base member samples based onSample Nos. 6 to 10.

As a result of concurrently having conducted the above thermal oxidationtreatment and thermally softening treatment, each of the polycrystallinesilicon base members became to have a heat accumulating layer comprisingthe thermal oxide layer (that is, the SiO₂ layer) thereon. The thicknessof the heat accumulating layer (that is, the SiO₂ layer) in each casewas found to be 3.0 μm.

As for the heat accumulating layer of each of the polycrystallinesilicon base member samples, evaluation was made of its surface stepstate while measuring it by means of the surface profiler by stylus inthe same manner as in Experiment E-1.

The evaluated results revealed that the surface step state of each ofSample Nos. 6 and 7 is ⊚, the surface step state of each of Sample Nos.8 and 9 is ∘, and the surface step state of Sample No. 10 is X.

As for each of the polycrystalline silicon base member samples obtainedin the above, on the surface of the heat accumulating layer, there wereformed a plurality of heat generating resistor each comprising HfB₂(size: 20 μm×100 μm, thickness: 0.16 μm, wiring density: 16 Pel (thatis, 16/mm)) and a plurality of Al electrodes (width: 20 μm, thickness:0.6 μm) each being connected to one of the heat generating resistorsusing the photolithography technique. Then, a protective layercomprising SiO₂ /Ta was formed above each portion where the heatgenerating resistor and electrode were formed by means of a conventionalsputtering technique. Thus, there was obtained five substrates forliquid jet recording head each being of the configuration shown in FIGS.1(A) and 1(B).

In the above, Sample No. 6 was found to be accompanied by a deformationwhich was caused at the time of the thermally softening treatmentwherein an excessively high softening temperature was employed. And inthe process of preparing a substrate for liquid jet recording head usingthis sample, a crack was occurred at the base member, and because ofthis, no practically acceptable substrate for liquid jet recording headcould be obtained.

As for each of the resultant four substrates for liquid jet recordinghead of Sample Nos. 7 to 10, a plurality of liquid pathways and a liquidchamber were formed using a dry film, followed by cutting with the useof a slicer to form a plurality of discharging outlets, whereby a liquidjet recording head of the configuration shown FIGS. 5(A) and 5(B) wasobtained.

As for each of the resultant four liquid jet recording heads, thedischarging durability test was conducted by repeatedly applying 1.1 Vth(Vth: discharging threshold voltage) and a driving pulse (a printingsignal) with a pulse width of 10 us to each of the heat generatingresistors to thereby discharge ink from each of the discharging outlets.

The evaluation of the durability of each of the liquid jet recordingheads was conducted by obtaining a survival rate of the heat generatingresistors, specifically, the number of the heat generating resistors notdisconnected versus the total number of the heat generating resistorswhen the integrated value of the driving pulses became each of 1×10⁷,1×10⁸ and 3×10⁸. The evaluated results are shown in each of the columnsof Sample Nos. 7 to 10 of Table 5-2.

From the evaluated results, it is understood that in the case of each ofthe four recording heads based on Sample Nos. 7 to 9, no cavitationdisconnection is occurred and the survival rate is 100% even after 3×10⁸times repetition of the driving pulse, but in the case of the recordinghead based on Sample No. 10, a cavitation disconnection is occurred atan early stage, and the survival rate is markedly low. Based on thesefacts, it was recognized that by forming a thermal oxide layer on thesurface of a polycrystalline silicon base member by concurrentlyconducting the thermally oxidation treatment and thermally softeningtreatment for the surface of the polycrystalline silicon base member ata temperature in the range of 1230° C. to 1330° C., there can be formeda desirable heat accumulating layer with a desirable surface whereinsteps are smoothed in a desirable state, and there can be obtained adesirable liquid jet recording head which provides superior results inthe discharging durability test.

Experiment E-3

In this experiment, studies were made of the effects of apolycrystalline silicon base member having a thermal oxide layer (a heataccumulating layer) formed in the same manner as in Experiment E-1wherein the surface of a polycrystalline silicon base member isthermally oxidized to form a thermal oxide layer and the thermal oxidelayer is then thermally softened, except that the thermal oxide layerformed by way of the thermal oxidation is doped with an impurity and theimpurity-doped thermal oxide layer is subjected to the thermallysoftening treatment.

Following the manner employed in Experiment B, there were obtainedfifteen polycrystalline silicon base member samples (Sample Nos. 11 to25) each being of 300×150×1.1 (mm) in size and having a mirror-groundsurface with a surface roughness of Rmax 150 Å.

On the surface of each of the polycrystalline silicon base members,there was formed a thermal oxide layer by thermally oxidizing thesurface of the polycrystalline silicon base member sample in the samemanner as in Experiment E-1. The resultant thermal oxide layer was dopedwith an impurity in the following manner.

That is, the impurity-doping for the thermal oxide layer (the SiO₂layer) was conducted using a conventional CVD technique. As thedopant-imparting source, there was used POCl₃ as a liquid source, and N₂gas as a carrier gas was introduced in a reaction chamber containingsaid liquid source to generate a gaseous atmosphere in a saturated statewhere the polycrystalline silicon base member sample having the thermaloxide layer thereon was placed. The period of time for diffusing thedopant into the sample was made to be 30 minutes in each case. Thedopant-diffusing temperature was made to be 1050° C. as for each of thesamples of Sample Nos. 11 to 15, 1000° C. as for each of the samples ofSample Nos. 16 to 20, and 950° C. as for each of the samples of SampleNos. 21 to 25. As for each of the resultants, the phosphorous content atthe surface was measured by means of a secondary ion mass spectrometer(trademark name: IMS-3F, produced by CAMECA Company)(hereinafterreferred to as SIMS). The measured results revealed that the phosphorouscontent at the surface is 5×10²¹ atoms/cm³ as for each of the samples ofSample Nos. 11 to 15 for which the dopant diffusion was conducted at1050° C.; 1×10²¹ atoms/cm³ as for each of the samples of Sample Nos. 16to 20 for which the dopant diffusion was conducted at 1000° C.; and1×10²⁰ atoms/cm³ as for each of the samples of Sample Nos. 21 to 25 forwhich the dopant diffusion was conducted at 950° C.

As for each of the fifteen resultants each having the thermal oxidelayer doped with the impurity, the thermal oxide later thereof wasthermally softened in the same manner as in Experiment E-1. Thethermally softening treatment in each case was conducted for a fixedperiod of time of an hour at a different temperature of 1230° C., 1230°C., 1180° C., 1130° C. or 1080° C. The softening temperature employed ineach case is shown in Table 5-3.

Thus, there were obtained fifteen polycrystalline silicon base membersamples based on Sample Nos. 11 to 25.

As a result of having conducted the above treatments, each of thepolycrystalline silicon base member samples became to have a heataccumulating layer comprising the thermal oxide layer (that is, the SiO₂layer) thereon. The thickness of the heat accumulating layer (that is,the SiO₂ layer) in each case was found to be 3.0 μm.

As for the heat accumulating layer of each of the polycrystallinesilicon base member samples, evaluation was made of its surface stepstate while measuring it by means of the surface profiler by stylus inthe same manner as in Experiment E-1.

The evaluated results revealed that the surface step state of each ofSample Nos. 19 and 23 is ∘, the surface step state of each of SampleNos. 20, 24 and 25 is X, and the surface step state of each of theremaining samples is ⊚.

As for each of the polycrystalline silicon base member samples obtainedin the above, on the surface of the heat accumulating layer, there wereformed a plurality of heat generating resistor each comprising HfB₂(size: 20 μm×100 μm, thickness: 0.16 μm, wiring density: 16 Pel (thatis, 16/mm)) and a plurality of Al electrodes (width: 20 μm, thickness:0.6 μm) each being connected to one of the heat generating resistorsusing the photolithography technique. Then, a protective layercomprising SiO₂ /Ta was formed above each portion where the heatgenerating resistor and electrode were formed by means of a conventionalsputtering technique. Thus, there was obtained fifteen substrates forliquid jet recording head each being of the configuration shown in FIGS.1(A) and 1(B).

As for each of the resultant substrates for liquid jet recording headbased on Sample Nos. 11 to 25, a plurality of liquid pathways and aliquid chamber were formed using a dry film, followed by cutting withthe use of a slicer to form a plurality of discharging outlets, wherebya liquid jet recording head of the configuration shown FIGS. 5(A) and5(B) was obtained.

As for each of the resultant fifteen liquid jet recording heads thedischarging durability test was conducted by repeatedly applying 1.1 Vth(Vth: discharging threshold voltage) and a driving pulse (a printingsignal) with a pulse width of 10 us to each of the heat generatingresistors to thereby discharge ink from each of the discharging outlets.

The evaluation of the durability of each of the liquid jet recordingheads was conducted by obtaining a survival rate of the heat generatingresistors specifically the number of the heat generating resistors notdisconnected versus the total number of the heat generating resistorswhen the integrated value of the driving pulses became each of 1×10⁷,1×10⁸ and 3×10⁸. The evaluated results are shown in each of the columnsof Sample Nos. 11 to 25 of Table 5-3.

As for each of the liquid jet recording heads based on Sample Nos. 11 to15, numerous disconnections were occurred at the heat generatingresistors even at the stage wherein the integrated value of the drivingpulses was small. As a result of observing such disconnected portionsusing a scanning electron microscope it was found that peelings arepresent between the thermal oxide SiO₂ layer and the heat generatingresistors. In the case of each of the liquid jet recording heads basedon Sample Nos. 11 to 15, it is considered that the temperature for theheat accumulating layer (the thermal oxide SiO₂ layer), on which theheat generating resistors are to be disposed, upon conducting thethermally softening treatment was lowered probably due to the highdopant content at the surface and a deformation was occurred at the basemember when the heat generating resistors were energized to 1100° C. interms of maximum temperature.

From the evaluated results as for each of the recording heads based onSample Nos. 16 to 25, it is understood that in the case of each of therecording heads based on Sample Nos. 20, 24 and 25, a cavitationdisconnection is occurred at an early stage, and the survival rate ismarkedly low, but in the case of each of the remaining recording headsbased on Sample Nos. 16-19, and 21-23, no cavitation disconnection isoccurred and the survival rate is 100% even after 3×10⁸ times repetitionof the driving pulse.

Based on these facts, it was recognized that pronounced advantages areprovided in the case where the thermal oxide layer formed on thepolycrystalline silicon member is doped with an impurity in such anamount that the softening temperature thereof is lowered to a relativelylow temperature of 1130° C. or above, such that effective elimination ofthe problems relating to occurrence of surface steps can be attained ata temperature which is lower by more than 100° C. in comparison with thecase where no impurity doping is conducted, the operation temperature ofthe treatment furnace used can be relatively lowered wherein thelifetime of the treatment furnace is eventually extended, and as aresult, a product can be provided at a reduced cost.

It was also found that the maximum temperature for conducting thethermally softening treatment is desired to be lower than 1330° C.wherein negative influences are not occurred due to a deformation at thepolycrystalline silicon base member, as well as in the case of each ofExperiment E-1 and Experiment E-2.

There was obtained a further finding that in the case where the sameconditions relating to the temperature and treating period of time forthe thermally softening treatment employed in the case where noimpurity-doping treatment is conducted are employed, the surfacesoftening of the thermal oxide later is facilitated to provide a moredesirable step-free surface state for the thermal oxide layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The principal feature of the present invention lies in a substrate forliquid jet recording head. The substrate is characterized by comprisinga polycrystalline silicon base member provided with a heat accumulatinglayer (a thermal oxide layer) with a smoothly flat surface. The heataccumulating layer is formed by subjecting the surface of apolycrystalline silicon member to thermal oxidation treatment andthermally softening treatment.

In the case where the base member of the above substrate is comprised ofa polycrystalline silicon member, the surface of the polycrystallinesilicon member is not flat due to its constituent crystal grains asdescribed in the foregoing experiments, and because of this, a thermaloxide layer formed thereon unavoidable becomes to have a surfaceaccompanied by surface steps.

The present invention has been accomplished based on the findingsobtained especially in the foregoing Experiment E which was conducted bythe present inventor in order to eliminate the problems relating to suchsurface step. The polycrystalline silicon base member having a heataccumulating layer with a smoothly flat surface according to the presentinvention can be realized by providing a base member comprising apolycrystalline silicon material and subjecting the surface of the basemember to thermal oxidation treatment and thermally softening treatmentto thereby form a heat accumulating layer with a smoothly flat surface.

In the present invention, since the polycrystalline silicon base memberhaving such a heat accumulating layer is used as a constituent of thesubstrate for liquid jet recording head, if an internal stress should beoccurred in the substrate due to an uneven shrinkage caused uponrepetition of heating and cooling, no problematic deformation isoccurred at the substrate.

The above thermally softening treatment can be conducted after a thermaloxide layer has been formed by thermally oxidizing the surface of apolycrystalline silicon base member or it can be conducted concurrentlytogether with the thermal oxidation treatment. In the case where thethermal oxidation treatment and thermally softening treatment areconcurrently conducted, the period of time required for the formation ofthe heat accumulating layer on the polycrystalline silicon base memberis markedly shortened in comparison with that in the case of forming theheat accumulating layer by individually conducting the thermal oxidationtreatment and thermally softening treatment.

In the case where the thermally softening treatment is independentlyconducted, it can be conducted by way of lamp heating using halogen lampor xenon lamp, or by way of continuous wave heating or pulse waveheating with laser of CO₂, YAG or Ar, or by way of continuous waveheating or pulse wave heating with electron beam, or by way of highfrequency heating. In this case, it is possible for the thermallysoftening treatment to be carried out only for given portions of thesurface of the polycrystalline silicon base member, for instance, onlyfor the surface portions on which heat generating resistors are to bedisposed. It is important that the thermally softening treatment isconducted at a temperature which is lower than the fusing point of apolycrystalline silicon material used as the base member. Specifically,the temperature at which the thermally softening treatment is conductedis desired to be in the range of 1230° C. to 1330° C., as described inthe foregoing Experiment E.

In the present invention, in the case where the thermal oxidationtreatment and the thermally softening treatment are individuallyconducted, the object of the present can be desirably attained by dopingthe thermal oxide layer formed by way of the thermal oxidation treatmentwith an appropriate impurity and subjecting the resultant to thethermally softening treatment. The thermally softening treatment in thiscase can be conducted at a temperature which is lower than that in thecase where thermally softening treatment is conducted without conductingthe impurity-doping treatment.

As the above impurity to be incorporated into the thermal oxide layerformed by way of the thermal oxidation treatment, any of theconventional elements which are generally used in the field ofsemiconductor such as P, B, As or the like can be selectively used. Theincorporation of such impurity into the thermal oxide layer may becarried out by a conventional impurity-introducing technique generallyemployed in the field of semiconductor. The concentration of theimpurity to be incorporated into the thermal oxide later is somewhatdifferent depending upon the kind of the impurity used. In general, itis should be properly decided with a due care about its upper limit sothat the heat accumulating layer (the thermal oxide layer) is notsoftened at a temperature to which the heat generating resistorsdisposed thereon are energized and also with a due care about its lowerlimit so that the heat accumulating layer can be softened in a desirablestate to provide a smoothly flat surface therefor.

The thermally softening treatment in the present invention is conductedprincipally aiming at eliminating surface steps occurred at the surfaceof the thermal oxide layer and providing a smooth surface state for thethermal oxide layer. The heat generating resistors disposed on thesmoothly flat surface of the thermal oxide layer provided as a result ofthe thermally softening treatment are ensured in terms of close contactwith the thermal oxide layer.

The present invention includes a substrate for liquid jet recording headin which the foregoing polycrystalline silicon-based base member isused, a liquid jet recording head provided with said substrate forliquid jet recording head, a liquid jet recording apparatus providedwith said recording head, and a process for producing said substrate forliquid jet recording head.

The substrate for liquid jet recording head to be provided according tothe present invention comprises a polycrystalline silicon-based basemember and an electrothermal converting body disposed on said basemember, said electrothermal converting body comprising a heat generatingresistor capable of generating thermal energy and a pair of wiringselectrically connected to said heat generating resistor, characterizedin that said base member has, on its surface, a thermal oxide layerwhich is formed by subjecting the surface of said base member to thermaloxidation treatment and thermally softening treatment.

The liquid jet recording head to be provided according to the presentinvention includes a liquid discharging outlet; a substrate for liquidjet recording head including an electrothermal converting bodycomprising a heat generating resistor capable of generating thermalenergy for discharging liquid from said discharging outlet and a pair ofwirings electrically connected to said heat generating resistor, saidpair of wirings being capable of supplying an electric signal forgenerating said thermal energy to said heat generating resistor; and aliquid supplying pathway disposed in the vicinity of said electrothermalconverting body of said substrate, characterized in that said substrateincludes a polycrystalline silicon-based base memer having, on thesurface of said base bember, a thermal oxide layer formed by subjectingthe surface of said base member to thermal oxidation treatment andthermally softening treatment.

The liquid jet recording apparatus to be provided according to thepresent invention includes (a) a substrate for liquid jet recording headincluding a liquid discharging outlet, an electrothermal converting bodycomprising a heat generating resistor capable of generating thermalenergy for discharging liquid from said discharging outlet and a pair ofwirings electrically connected to said heat generating resistor, saidpair of wirings being capable of supplying an electric signal forgenerating said thermal energy to said heat generating resistor, and (b)a liquid supplying pathway disposed in the vicinity of saidelectrothermal converting body of said substrate, characterized in thatsaid substrate (a) includes a polycrystalline silicon-based base memerhaving, on the surface of said base bember, a thermal oxide layer formedby subjecting the surface of said base member to thermal oxidationtreatment and thermally softening treatment.

The process to be provided according to the present invention is forproducing a substrate for liquid jet recording head wherein anelectrothermal converting body is disposed on a base member, saidelectrothermal converting body comprising a heat generating resistor anda pair of wirings electrically connected to said heat generatingresistor, which is characterized by including the steps of using amember composed of a polycrystalline silicon material as said basemember and subjecting said polycrystalline silicon member to thermaloxidation treatment for forming a thermal oxide layer on the surface ofsaid polycrystalline silicon member and to thermally softening treatmentfor softening the surface of said thermal oxide layer to provide asmoothly flat surface state for said thermal oxide layer, wherebyforming a heat accumulating layer with a smoothly flat surface on saidpolycrystalline silicon member.

A typical example of the base member constituting the substrate forliquid jet recording head in the present invention, there can bementioned a base member composed of a polycrystalline silicon material(this will be hereinafter referred to as a polycrystalline silicon basemember). The polycrystalline silicon base member is rather difficult tobe deformed in comparison with a single crystal silicon base member.Because of this, as described in the foregoing experiments, thepolycrystalline silicon base member provides a prominent effect in thatthe elongation of a recording head, which is hardly attained in the caseof using a single crystal silicon base member, can be effectivelyattained.

In the present invention, the use of the polycrystalline silicon basemember in the substrate for liquid jet recording head provides furtheradvantages such that the substrate can be lengthened to a desired lengthwherein, as described in the foregoing Experiment B, the warp magnitudeis slight and is smaller than that of the single crystal silicon basemember, and therefore, an elongated liquid jet recording head which isfree of the problems relating to occurrence of warpage can be easily andeffectively obtained. The elongated recording head is free of theproblems relating to occurrence of defects for an image recorded whichare caused in the case of an elongated liquid jet recording headobtained by integrating a plurality of miniature recording heads.Further, the elongated liquid jet recording head according to thepresent invention can attain a desirable recording apparatus capable ofperforming high speed recording.

The warp magnitude is, as described in the foregoing Experiment C,proportional to the mean crystal grain size of the polycrystallinesilicon material constituting the base member. In order to attain adesirable yield in the production of the liquid jet recording headaccording to the present invention, the polycrystalline silicon materialconstituting the base member for the substrate for liquid jet recordinghead is desired to be preferably of 8 um or less, more preferably of 2um or less in terms of mean crystal grain size. To use a polycrystallinesilicon base member having a mean crystal grain size in said rangeenables to obtain a desirable substrate for liquid jet recording headwhich is free of occurrence of warpage, and as a result, an elongatedliquid jet recording head capable of providing a high quality recordedimage at a high recording speed can be easily and effectively attained.

On the polycrystalline silicon base member for the substrate for liquidjet recording head, a heat generating resistor layer and wirings aredisposed. Therefore, the polycrystalline silicon base member is desirednot to have defects such as pits, protrusions, or the like at thesurface thereof. In the case where these defects are present at thesurface of the base member, such defect is liable to lead to causing adisconnection or shortcircuit for the heat generating resistor layerformed thereon. As described in the foregoing Experiment D, in order toattain a high production yield and in order to attain desirablerecording characteristics as for the liquid jet recording head, thepolycrystalline silicon base member used for the substrate for liquidjet recording head is desired to be such that the number of such defectsof about 1 um in diameter present at the surface thereof is preferably10/cm² or less, more preferably 5/cm² or less.

In the following, description will be made of an embodiment of thesubstrate for liquid jet recording head according to the presentinvention.

FIG. 1(A) is a schematic plan view illustrating the principal part of anexample of the substrate for liquid jet recording head according to thepresent invention. FIG. 1(B) is a schematic cross-sectional view, takenalong the line X-X' in FIG. 1(A). FIG. 2 is a schematic cross-sectionalview illustrating a base member constituting said substrate for liquidjet recording head.

A substrate 8 for liquid jet recording head has, on a polycrystallinesilicon base member 1, a electrothermal converting body comprising aheat generating resistor 2a capable of generating thermal energy fordischarging a liquid recording medium and a pair of wirings 3a and 3belectrically connected to said heat generating resistor 2a.

After having laminated a heat generating resistor 2 comprising amaterial with a relatively large volume resistivity and an electrodelayer 3 comprising a material having a good electroconductivity on thepolycrystalline silicon base member 1, for example, by a conventionalsputtering technique, the heat generating resistor 2a and the wirings 3aand 3b are formed respectively in a given pattern by way of thephotolithography process. The heat generating resistor thus formedserves to energize upon applying an electric signal to the heatgenerating resistor through the wirings 3a and 3b.

The material constituting the heat generating resistor layer 2 caninclude hafnium boride (HfB₂), tantalum nitride (Ta₂ N), rubidium oxide(RuO₂), Ta--Al alloy, and Ta--Al--Ir alloy, other than these, variousmetals, alloys, metal compounds, and cermets.

The material constituting the electrode layer 3 can include metalshaving a high electroconductivity such as aluminum, gold and the like.

The substrate for liquid jet recording head 8 includes a protectivelayer 4 which is disposed so as to cover the wirings 3a and 3b and theheat generating resistor 2a. The protective layer 4 is disposed for thepurpose of preventing the heat generating resistor 2a and the wirings 3aand 3b from suffering not only from electric corrosion but also fromelectric breakdown which will be occurred when they are contacted withink or when ink is permeated thereinto. The protective layer may beformed of an electrically insulative material such as SiO₂, SiC, Si₃ N₄,or the like. The protective layer may be of a multilayered structure. Inthis case, the protective layer may take a stacked structure, forexample, comprising a layer formed of said electrically insulativematerial and a layer formed of Ta or Ta₂ O₅ being stacked on the formerlayer.

The above embodiment of the liquid jet recording head is of theconfiguration wherein the direction in which a liquid recording mediumis discharged from the discharging outlet and the direction in which aliquid recording medium is supplied toward the heat Generating resistorare substantially the same, but it can take another configurationwherein the two directions are different from each other (for instance,they are substantially perpendicular to each other).

In the following, description will be made of an embodiment of a liquidjet recording head in which the above described substrate is used.

The principal configuration of the recording head previously has beenexplained with reference to FIG. 5(A) and FIG. 5(B). Herein, descriptionagain will be made.

A liquid pathway 6 for supplying ink is formed in the vicinity of eachheat generating resistor 2a by connecting a top plate 5 to thesubstrate. The ink in the liquid pathway is heated by the heatgenerating resistor to cause a bubble, wherein the ink is dischargedthrough a discharging outlet 7 by virtue of a pressure caused uponforming the bubble, whereby performing recording.

In the configuration shown in FIG. 5(A) and FIG. 5(B), there is shown anarrangement in which one heat generating resistor corresponds to onedischarging outlet. However, the recording head of the present inventionis not limited to this configuration only. That is, any otherconfigurations including, for instance, a configuration in which aplurality of heat generating resistors correspond to one dischargingoutlet, can be employed as long as the foregoing substrate can beapplied. Further, in the configuration shown in FIG. 5(A) and FIG. 5(B),the substrate surface on which the heat generating resistors arearranged is substantially in parallel to the direction in which the inkis discharged. The recording head of the present invention is notlimited to this configuration only, but may take such a configurationthat the direction in which the ink is discharged is in a relationshipof crossing with the substrate surface.

The liquid jet recording head of the present invention may be designedsuch that it can be mounted in an apparatus capable of being a recordingapparatus, for instance, in a detachable state, wherein ink is suppliedfrom a separate ink container through a tube. Other than this, it may bedesigned such that it can be detachably amounted in an apparatus capableof being a recording apparatus while being detachably connected to aseparate ink container.

As the liquid recording medium usable in the recording head of thepresent invention, there can be used various kinds. Examples of suchliquid recording medium are liquid recording mediums having an inkcomposition comprising 0.5 to 20 wt. % of dye, 10 to 80 wt. % ofwater-soluble organic solvent such as polyhydric alcohol, polyalkyleneglycol, or the like, and 10 to 90 wt. % of water. As a specific exampleof such ink composition, there can be mentioned one comprising 2.3 wt. %of C.I. food black, 25 wt. % of diethylene glycol, 20 wt. % ofN-methyl-2-pyrrolidone, and 52 wt. % of water.

FIG. 6 is an appearance perspective view illustrating an example of anink jet recording apparatus IJRA in which the recording head of thepresent invention is used as an ink jet head cartridge IJC. In FIG. 6,reference numeral 120 indicates the ink jet head cartridge IJC providedwith nozzle groups capable of discharging ink to the face of a recordingmember transported onto a platen 124. Reference numeral 116 indicates acarriage HC which serves to hold the IJC 120. The carriage HC isconnected to a part of a driving belt 118 capable of transmitting adriving force such that it can be slidably moved together with two guideshafts 119A and 119B arranged in parallel with each other. By this, theIJC 120 is allowed to move back and forth along the entire of therecording member.

Herein, although the ink jet head cartridge as the recording headcomprises a miniature recording head, it is a matter of course that theelongated recording head of the present invention, which is designed,for example, to be of a so-cally full line type capable of performingrecording for a given recording width of a recording member used, can beused. In the case of using such elongated recording head, there can beattained a recording apparatus in which the foregoing advantages of theelongated recording head, namely, an advantage of being free of warpage,an advantage of being free of the problems of causing defects for animage recorded which are found in the case of using a relatively shortrecording head, and an advantage of making it possible to conduct highspeed recording, are fully effectively used.

Reference numeral 126 indicates a head restoring device which isdisposed at one end of the moving passage of the IJC 120, specificallyat the position opposite the home position. The head restoring device120 is operated by virtue of a driving force transmitted through adriving mechanism 123 from a motor 122, whereby capping the IJC 120. Inrelation to the capping for the IJC 120 by a cap member 126A of the headrestoring device, the discharge restoration treatment of removingadhesive ink in the nozzles is conducted by way of ink sucking by meansof an appropriate sucking means disposed in the head restoring device126 or by way of ink pressure transportation by means of an appropriatepressurizing means whereby forcibly discharging the ink through thedischarging outlets. When the recording is terminated, the IJC isprotected by capping it.

Reference numeral 130 indicates a cleaning blade comprising a wipingmember formed of a silicon rubber which is arranged at a side face ofthe head restoring device 126. The cleaning blade 130 is supported by ablade supporting member 130A in a cantilever-like state. As well as inthe case of the head restoring device 126, the cleaning blade 130 isoperated by virtue of a driving force transmitted through the drivingmechanism 123 from the motor 122, wherein the cleaning blade is madecapable of contacting with the discharging face of the IJC 120. By this,the cleaning blade 130 is projected into the moving passage of the IJC120 timely with the recording performance of the IJC 120 or after thedischarge restoration treatment using the head restoring device havingbeen completed to thereby remove dew drops, wettings, dirts, and thelike deposited on the discharging face of the IJC 120.

The recording apparatus is also provided with an electric signalapplying means for applying an electric signal to the recording head.Further, the recording apparatus includes, other than the aboveembodiment of conducting recording to a recording member, an embodimentcomprising a textile printing apparatus of recording patterns to afabric or the like. In the case of the textile printing apparatus, it isnecessary to conduct recording to a fabric with an extremely wide width,wherein the elongated recording head of the present invention is veryeffective.

Other Embodiments

The present invention provides prominent effects in an ink jet recordinghead and ink jet recording apparatus of the system in which ink isdischarged utilizing thermal energy. As for the representativeconstitution and the principle, it is desired to adopt such fundamentalprinciple as disclosed, for example, in U.S. Pat. No. 4,723,129 or U.S.Pat. No. 4,740,796. While this system is capable of applying either theso-called on-demand type or the continuous type, it is particularlyeffective in the case of the on-demand type because, by applying atleast one driving signal for providing a rapid temperature riseexceeding nucleate boiling in response to recording information to anelectrothermal converting body disposed for a sheet on which liquid(ink) is to be held or for a liquid pathway, the electrothermalconverting body generates thermal energy to cause film boiling on a heatacting face of the recording head and as a result, a gas bubble can beformed in the liquid (ink) in a one-by-one corresponding relationship tosuch driving signal.

By way of growth and contraction of this gas bubble, the liquid (ink) isdischarged trough a discharging outlet to form at least one droplet. Itis more desirable to make the driving signal to be of a pulse shape,since in this case, growth and contraction of a gas bubble take placeinstantly and because of this, there can be attained discharging of theliquid (ink) excelling particularly in responsibility.

As the driving signal of pulse shape, such driving signal as disclosedin U.S. Pat. No. 4,463,359 or U.S. Pat. No. 4,345,262 is suitable.Additionally, in the case where those conditions disclosed in U.S. Pat.No. 4,313,124, which relates to the invention concerning the rate oftemperature rise at the heat acting face, are adopted, further improvedrecording can be performed.

As for the constitution of the recording head, the present inventionincudes, other than those constitutions of the discharging outlets,liquid pathways and electrothermal converting bodies in combination(linear liquid flow pathway or perpendicular liquid flow pathway) whichare disclosed in each of the above mentioned patent documents, theconstitutions using such constitution in which a heat acting portion isdisposed in a curved region as disclosed in U.S. Pat. No. 4,558,333 orU.S. Pat. No. 4,459,600.

In addition, the present invention may effectively take a constitutionbased on the constitution in which a slit common to a plurality ofelectrothermal converting bodies is used as a discharging portion of theelectrothermal converting bodies which is disclosed in JapaneseUnexamined Patent Publication No. 123670/1984 or another constitutionbased on the constitution in which an opening for absorbing a pressurewave of thermal energy is made to be corresponding to a dischargingportion which is disclosed in Japanese Unexamined Patent Publication No.138461/1984.

Further, in the case of an ink jet recording apparatus comprising afull-line type recording head having a length corresponding to the widthof a maximum recording member onto which recording can be performed, theforegoing effects are more effectively provided. The present inventionis effective also in the case where a recording head of the exchangeablechip type wherein electric connection to an apparatus body or supply ofink from the apparatus body is enabled when it is mounted on theapparatus body or other recording head of the cartridge type wherein anink tank is integrally disposed on the recording head itself isemployed.

Furthermore, the present invention is extremely effective not only in arecording apparatus which has, as the recording mode, a recording modeof a main color such as black but also in a recording apparatus whichincludes a plurality of different colors or at least one of fullcolorsby color mixture, in which a recording head is integrally constituted ora plurality of recording heads are combined.

In the above-described embodiments of the present invention, explanationhas been made with the use of liquid ink, but it is possible to use suchink that is in a solid state at room temperature or other ink whichbecomes to be in a softened state at room temperature in the presentinvention. In the foregoing ink jet apparatus, it is usual to adjust thetemperature of ink itself in the range of 30° C. to 70° C. such that theviscosity of ink lies in the range capable of being stably discharged.In view of this, any ink can be used as long as it is in a liquid stateupon the application of a use record signal. It is also possible tothose inks having a property of being liquefied, for the first time,with thermal energy, such as ink that can be liquefied and discharged inliquid state upon the application of thermal energy depending upon arecord signal or other ink that can start its solidification beforehandat the time of its arrival at a recording member in order to prevent thetemperature of the head from raising due to thermal energy purposelyused as the energy for a state change of ink from solid state to liquidstate or in order to prevent ink from being vaporized by solidifying theink in a state of being allowed to stand. In the case of using theseinks, they can be used in such a manner as disclosed in JapaneseUnexamined Patent Publication No. 56847/1979 or Japanese UnexaminedPatent Publication No. 71260/1985 in which ink is maintained in concavedportions or penetrations of a porous sheet in a liquid state or in asolid state and the porous sheet is arranged to provide a configurationopposite the electrothermal converting body.

EXAMPLES

In the following, the features and advantages of the present inventionwill be described in more detail with reference to the followingexamples, but the scope of the present invention is not restricted bythese examples.

Example 1

(preparation of a ploycrystalline silicon base member for a substratefor liquid jet recording head)

A polycrystalline silicon ingot as the stating material was prepared inthe following manner. That is, there was firstly provided a high puritypolycrystalline silicon material obtained in accordance with theconventional precipitation reaction manner through hydrogen reductionand pyrolysis, which is usually employed in the production of a singlecrystal silicon material. The polycrystalline silicon material was thenintroduced into a quartz crucible wherein it was fused at 1420° C. Theresultant fused material was poured into a casting mold made of graphitewherein it was cooled, to thereby obtain a polycrystalline silicon ingotof 80 cm in square size. In this case, no release agent was used.

The ingot thus obtained was quarried at the position thereof with a meancrystal grain size of 2 mm by means of a milti-wire saw, to obtaintwelve plate samples each having a different size shown in one of thecolumns Sample No. 1 to Sample No. 12 of Table 6. Each of the twelveplate samples was subjected to lapping treatment to remove an about 30μm thick surface portion to thereby provide a flat surface therefor. Theend portions of the resultant were chanferred by means of a bevelingmachine, followed by subjecting to polishing treatment using a singleside polishing machine produced by Speedfarm Kabushiki Kaisha, tothereby obtain a mirror-ground member with a surface roughness of Rmax150 Å. In this case, the polishing treatment was conducted without usingan alkali, in order to prevent a surface step from being formed, whichwill be occurred due to that the etching by an alkali componentcontained in the abrasive material has a crystal orientation dependency.Thus, there were obtained twelve mirror-ground polycrystalline siliconplate samples.

As for each of the resultant polycrystalline silicon plate samples,namely, the polycrystalline silicon base members, its surface state wasexamined by the same surface examination manner using the inspectionsystem for substrate surface employed in the foregoing Experiment D. Asa result, each of the base members was found to be of less than 1/cm² interms of the number of defects based on irregularities in the maximumdetectable range of more than 1 um in diameter at all the measuredpoints.

Further, each of the base member samples was examined with respect itssurface flatness using a surface profiler by stylus produced byLasertech Kabushiki Kaisha. As a result, each of the base member sampleswas found to be free of occurrence of a surface step.

Four of the polycrystalline silicon base member samples were chosen, andas for each of them, a SiO₂ film as the heat accumulating layer wasformed on the surface thereof by subjecting the surface of the sample tothermal oxidation treatment by way of the pyrogenic method. In thiscase, the following film-forming conditions were employed:

thermal oxidation temperature: 1150 20 C.,

inner pressure of the furnace: 1 atm., and

period of the thermal oxidation treatment: 14 hours.

Then, as for each of the four resultant base member samples each havingthe SiO₂ layer thereon, the surface of SiO₂ layer was flattened bysubjecting the SiO₂ layer to thermally softening treatment. Thethermally softening treatment in this case was conducted under thefollowing conditions:

thermally softening temperature: 1330° C.,

inner pressure of the furnace: 1 atm., and

period of the thermally softening treatment: 1 hour.

In this way, there were obtained four polycrystalline silicon work inprocess samples (Sample No. 1 to Sample No. 4) for a substrate forliquid jet recording head, each having a 3 μm thick thermal oxide layer(a SiO₂ layer) as the heat accumulating layer.

In addition, four of the remaining eight polycrystalline silicon basemember samples were chosen, and as for each of them, the foregoingthermal oxidation treatment and thermally softening treatment wereconcurrently conducted under the following conditions, to thereby form astep-free heat accumulating layer on the surface of the base membersample.

heat treatment temperature: 1150° C.,

inner pressure of the furnace: 1 arm., and

heat treatment period: 7 hours.

In this way, there were obtained four polycrystalline silicon work inprocess samples (Sample No. 5 to Sample No. 8) for a substrate forliquid jet recording head, each having a 3 μm thick thermal oxide layer(a SiO₂ layer) as the heat accumulating layer.

Finally, as for each of the remaining four base member samples, a SiO₂film as the heat accumulating layer was formed on the surface thereof bysubjecting the surface of the sample to thermal oxidation treatment byway of the pyrogenic method. Successively, an impurity in gaseous statewas diffused into the SiO₂ layer thus formed. The thermal oxidationtreatment and the impurity diffusion were conducted under the followingrespective conditions:

the conditions for the thermal oxidation treatment:

thermal oxidation temperature: 1150° C.,

inner pressure of the furnace: 1 arm., and

thermal oxidation period: 14 hours.

the conditions for the impurity diffusion:

diffusion source: POCl₃,

diffusion manner: low pressure thermal-induced CVD process, and

diffusion temperature: 1000° C.

As a result of measuring the content of P diffused at the surface ofeach polycrystalline silicon base member sample by the SIMS, thep-content was found to be 1×10²¹ atoms/cm³ in every case.

Then, as for each of the four resultant base member samples each havingthe SiO₂ layer thereon, the surface of SiO₂ layer was flattened bysubjecting the SiO₂ layer to thermally softening treatment. Thethermally softenin_(G) treatment in this case was conducted under thefollowing conditions:

thermally softening temperature: 1330° C.,

inner pressure of the furnace: 1 atm., and

period of the thermally softening treatment: 1 hour.

In this way, there were obtained four polycrystalline silicon work inprocess samples (Sample No. 9 to Sample No. 12) for a substrate forliquid jet recording head, each having a 3 um thick thermal oxide layer(a SiO₂ layer) as the heat accumulating layer.

As for the twelve samples of Sample Nos. 1 to 12 thus obtained,evaluation was made of the surface step state of the heat accumulatinglayer while measuring it by means of a conventional surface profiler bystylus. The condition for the measurement and the criteria for theevaluation were made as follows.

The measurement conditions:

the stylus scanning distance: 10 mm,

the number of the positions measured: 15 positions as for each sample,and

the position measured: 15 intersections of the three linear lines bywhich the short side of 150 mm in width is divided into four equal zonesand the five linear lines by which the long side of 600 mm, 500 mm, 400mm or 300 mm in length is divided into six equal zones as for eachsample.

The evaluation criteria:

⊚: the case where the maximum step height among the 15 measuredpositions is between 0 μm and less than 0.05 μm,

∘: the case where the maximum step height among the 15 measuredpositions is between 0.05 μm and less than 0.1 μm, and

X: the case where the maximum step height among the 15 measuredpositions is more than 0.1 μm.

The evaluated results revealed that all the samples of Sample Nos. 1 to12 are , and each of them has a smoothly flat surface wherein steps aredesirably flattened.

Then, as for each of the twelve samples of Sample Nos. 1 to 12, usingthe photolithography technique, there were formed, on the surfacethereof, a plurality of heat generating resistors each comprising HfB₂(size: 20 μm×100 μm, thickness: 0.16 μm, pitch interval: 63.5 μm) and aplurality of A1 electrodes (width: 20 μm, thickness: 0.6 μm) each beingconnected one of the heat generating resistors. Then, a protective layercomprising SiO₂ /Ta (the thickness of the SiO₂ film: 1.3 μm, thethickness of the Ta film: 0.5 μm) was formed above each portion, wherethe heat generating resistor and electrode were formed, by means of aconventional sputtering technique. Thus, there were obtained twelvesubstrates for liquid jet recording head (Sample No. 1 to Sample No. 12)each having the configuration shown in FIGS. 1(A) and 1(B).

Successively, as for each of the resultant twelve substrates for liquidjet recording head, a plurality of liquid pathways were formed inaccordance with the photolithography technique using a photosensitivedry film wherein exposure is conducted. Herein, in each case, evaluationwas conducted by examining of whether those ink pathways could beprecisely formed upon the exposure processing and obtaining an exposurefitness proportion.

Particularly, as for each substrate sample, 15 patten samples for liquidjet recording head each comprising a plurality of ink pathways for inkdischarging were formed, wherein each of the 15 pattern samples for eachof Samples Nos. 1, 5 and 9 comprising 8576 ink pathways, each of the 15pattern samples for each of Samples Nos. 2, 6 and 10 comprising 7244 inkpathways, each of the 15 pattern samples for each of Samples Nos. 3, 7and 11 comprising 5504 ink pathways, and each of the 15 pattern samplesfor each of Samples Nos. 4, 8 and 12 comprising 4288 ink pathways.

As for each of the resultant samples of Sample No. 1 to Sample No. 12,an exposure fitness proportion was obtained on the basis of the criteriain that the case where a pattern defect was occurred with regard to atleast one discharging outlet pattern as a result of the focusingposition having been deviated due to a warpage of the base member amongthe 15 pattern samples is made to be unfitness, and the case where nosuch pattern defect was occurred is made to be fitness. The resultsobtained are collectively shown in Table 6.

As apparent from the results shown in Table 6, it is understood that allthe resultant samples of Sample No. 1 to Sample No. 12 are of 100% interms of exposure fitness proportion. It is also understood that sincethe thermal oxide layer is thermally softened to provide a smoothlyflattened surface, the heat generating resistors formed thereon excel inclose contact with the thermal oxide layer in every case.

Comparative Example 1

(preparation of a single crystal silicon base member for a substrate forliquid jet recording head)

There was firstly provided a single crystal silicon ingot as thestarting material. Using this single crystal silicon ingot and inaccordance with the same manner employed in Example 1, there wereobtained four mirror-ground single crystal silicon base member sampleseach having a different size shown in one of the columns Sample No. 1 toSample No. 4 of Table 8 and having a surface roughness of Rmax 150 Å(Comparative Sample No. 1 to Comparative Sample No. 4). In each case,the polishing treatment was conducted with the addition of alkali. Asfor each of the resultants, there was formed a 3.0 μm thick thermaloxide heat accumulating layer by thermally oxidizing the surface thereofby the pyrogenic method in the same manner employed in Example 1, exceptthat the thermally softening treatment was not conducted. Thus, therewere obtained four work in process samples for a substrate for liquidjet recording head (Comparative Sample No. 1 to Comparative Sample No.4).

Using each of the four resultant samples, there were obtained fourcomparative substrate samples for liquid jet recording head by repeatingthe procedures of Example 1 (Comparative Sample No. 1 to ComparativeSample No. 4).

As for each of the resultant liquid jet recording head substrate samplesof Comparative Sample No. 1 to Comparative Sample No. 4, an exposurefitness proportion was evaluated in the same manner employed inExample 1. The results obtained are collectively shown in Table 8.

As apparent from the results shown in Table 8, it is understood thatComparative Sample No. 2 is of a reduced value in terms of exposurefitness proportion, Comparative Sample No. 1 is substantially unfitness,and each of Comparative Samples Nos. 3 and 4 each being relatively shortin length is 100% in terms of fitness proportion.

Example 2

(preparation of a liquid jet recording head using a polycrystallinesilicon substrate)

In this example, using each of the twelve liquid jet recording headsubstrate samples (Sample No. 1 to Sample No. 12) shown in Table 6 whichwere prepared by repeating the procedures of Example 1, there wereprepared twelve liquid jet recording heads of the configuration shown inFIG. 3 in the following manner.

As for each of the liquid jet recording head substrate samples, aplurality of ink pathways were formed thereon in accordance with thephotolithography technique using a photosensitive dry film. Using aslicer, the resultant was cut into a plurality of head units whileforming a plurality of discharging outlets. Then, the discharging outletface was polished to remove defects such as chippings caused at the timeof the cutting treatment. Thus, as for each of the liquid jet recordinghead substrate samples, there were obtained 15 liquid jet recording headworks in process. As for each of the 15 works in process obtained ineach case, ICs for driving the heat generating resistors wereelectrically connected to the wirings in accordance with the flip chipbonding technique, to thereby obtain a liquid jet recording head with adischarging outlet pitch interval of 63.5 um.

In this way, as for each of the liquid jet recording head substratesamples based on Sample No. 1 to Sample No. 12, there were obtained 15liquid jet recording head samples (the twelve groups each comprising the15 liquid jet recording heads based on each of Sample No. 1 to SampleNo. 12 will be hereinafter referred to as Sample No. 1', to Sample No.12', respectively).

As a result of conducting evaluation of the production process yield asfor each of Sample No. 1' to Sample No. 12', there were obtained theresults shown in Table 7, wherein the mark ∘ indicates the case whereinthe production yield is within a production yield previously estimatedbased on the number of discharging outlets, and the mark X indicates thecase wherein the production yield is inferior to the production yieldpreviously estimated based. From these results, it was found that eachof the liquid jet recording head samples of Sample No. 1' to Sample No.12' is within a normal level in terms of defect occurrence.

Then, as for each of Sample No. 1' to Sample No. 12', one liquid jetrecording head was randomly chosen, and it was dedicated for dischargedurability test. The durability test was conducted by repeatedlyapplying 1.1 Vth (Vth: discharging threshold voltage) and a drivingpulse (a printing signal) with a pulse width of 10 us to each of theheat generating resistors whereby discharging ink from each of thedischarging outlets.

The evaluation in the durability test was conducted by obtaining asurvival rate of the heat generating resistors, specifically, the numberof the heat generating resistors not disconnected versus the totalnumber of the heat generating resistors, when the integrated value ofthe driving pulses became each of 1×10⁷, 1×10⁸ and 3×10⁸. The evaluatedresults are collectively shown in Table 7.

As apparent from the results shown in Table 7, it is understood that thesurvival rate is 100% even after 3×10⁸ times repetition of the drivingpulse and thus, the durability is satisfactory in every case.

Successively, as for each of Sample No. 1' to Sample No. 12', anotherone liquid jet recording head was randomly chosen, and it was dedicatedfor evaluation of a printing performance, wherein a precision betweenthe printed dots and appearance of uneven density were evaluated.

There was used ink of the following composition:

dye: C.I. direct black 19--3 wt. %,

diethylene glycol--25 wt. %,

N-methyl-2-pyrrolidone--20 wt. %, and

ion-exchanged water--52 wt. %.

In this evaluation, there was used a paper with a bleeding probabilityadjusted to be in a given range. The paper was scanned perpendicularlyto the discharging direction of the liquid jet recording head whiledischarging ink from all the nozzles, to thereby obtain a printed samplehaving four different printed widths in the nozzle arrangement directionand with a printed area of 200 mm in the direction in which the paperwas moved. In this case, the paper moving speed was adjusted so that theprinting dot interval became 63.5 μm with a discharging frequency of 1KHz. The head driving conditions were made as follows.

voltage applied to the heat generating resistor: 1.1 Vth (Vth:discharging threshold voltage)

driving frequency: I KHz (the voltage applying interval to the heatgenerating resistor)

pulse width: 10 μm (the period of applying one pulse to the heatgenerating resistor)

In Table 7, there is shown a printing width as for each of the liquidjet recording head samples.

As for each printed sample obtained by each of the liquid jet recordinghead samples, evaluation was conducted with respect to printingprecision and appearance of uneven density in the following manner.

Evaluation of printing precision:

As for each printed sample, the printed dot interval (the intervalbetween the dot centers) was observed using a micrometer microscope,whereby a variation range was examined. In this case, the observationwas conducted at 10 randomly selected positions each having an area of 2cm in square size on the printed sample, wherein the directionperpendicular to the paper moving direction was made to be X and thepaper moving direction was made to be Y, and the case where as for allthe 10 positions each being of 2 cm in square size, the dot interval inthe X direction and that in the Y direction were within a range of 43.5μm to 83.5 μm was evaluated as being fitness.

As a result, each of Sample No. 1' to Sample No. 12' was found to befitness.

Evaluation of appearance of uneven density:

Each printed sample was evaluated with respect to appearance of unevendensity using a Macbeth densitometer. In this case, the entire area ofthe printed sample was read out by the binary image processing by CCDline sensor system, wherein the optical density was measured as forevery I cm width in the direction perpendicular to the paper movingdirection. In this evaluation, the case where the optical densities ofthe adjacent regions were within 0.2 was evaluated as being fitness.

As a result, each of Sample No. 1' to Sample No. 12' was found to befitness.

Comparative Example 2

(preparation of a liquid jet recording head using a single crystalsilicon substrate)

In this comparative example, using each of the four comparative liquidjet recording head substrate samples (Comparative Sample No. 1 toComparative Sample No. 4) shown in Table 8 which were prepared byrepeating the procedures of Comparative Example 1, there were preparedfour comparative liquid jet recording head samples (Comparative SampleNo. 1' to Comparative Sample No. 4') in the same manner employed inExample 2.

As for each of the resultant samples of Comparative Sample No. 1' toComparative Sample No. 4', the production process yield was evaluated inthe same manner as in Example 2. The results obtained are shown in Table9. Shown in the column relating to the production yield of Table 9 arethe results of the evaluation conducted based on the following criteria.

X: the case wherein no practically acceptable liquid jet recording headis found,

Δ: the case wherein the number of practically acceptable liquid jetrecording heads is few, and

∘: the case wherein the production yield is within a value previouslyestimated based on the number of nozzles.

From the results shown in Table 9, the following facts are understood.That is, no practically acceptable liquid jet recording head can beobtained in the case of Comparative Sample No. 1'; the production yieldfor a practically acceptable liquid jet recording head is extremely lowin the case of Comparative Sample No. 2'; and a desirable productionyield is provided in the case of each of Comparative Sample No. 3' andComparative Sample No. 4'.

Then, as for each of the comparative liquid jet recording head samplesof Comparative Sample No. 2' to Comparative Sample No. 4', evaluationwas conducted with respect to discharging durability, and printingprecision and appearance of uneven density in terms of printingperformance in the same manner as in Example 2. As a result, each of thepractically acceptable liquid jet recording head samples of ComparativeSamples Nos. 2', 3' and 4' was found to be fitness with regard to eachof the evaluation items of discharging durability, and printingprecision and appearance of uneven density in terms of printingperformance.

Comparative Example 3

(preparation of a liquid jet recording head using a single crystalsilicon substrate)

In this comparative example, two liquid jet recording head samples ofComparative Sample No. 4' shown in Table 9, which were prepared byrepeating the procedures of Comparative Example 2, were integrated toobtain a liquid jet recording head unit with 8576 discharging outlets(Comparative Example No. 4", see Table 10).

The head unit was prepared in the following manner. That is, one of theliquid jet recording head samples was was fixed to a face of an aluminumsupport member, and the remaining liquid jet recording head sample wasarranged on and fixed to the other face of the support member such thatthe discharging outlets of the two liquid jet recording heads werearranged to correspond to each other precisely as much as possible alongthe entire length of the liquid jet recording head unit.

The resultant liquid jet recording head unit was evaluated with respectto discharging durability, and printing precision and appearance ofuneven density in terms of printing performance in the same manner as inExample 2. As a result, it was found to be fitness with respect todurability. But it was found to be unfitness with respect to printingprecision. The reason for this was found to be due to the influencebased on an error in the assembly of the two heads. Further, as for theevaluation with respect to appearance of uneven density, it was found tobe unfitness. The reason for this was found to be due to a difference inthe Vth (discharging threshold voltage) among the two heads.

The results obtained are collectively shown in Table 10.

                  TABLE 1                                                         ______________________________________                                                          the presence or                                                               absence of  surface                                                           alkali at the                                                                             rough- step at                                  Sample            time of primary                                                                           ness   grain                                    No.   Si-base member                                                                            polishing   R.sub.max (Å)                                                                    boundary                                 ______________________________________                                        1     single crystal                                                                            present     150    --                                       2     single crystal                                                                            absent      150    --                                       3     polycrystalline                                                                           present     150    occurred                                                                      (maximum                                                                      0.2 μm)                               4     polycrystalline                                                                           absent      150    not                                                                           occurred                                 ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                                      maximum warp magnitude in                                       Sample base member size                                                                           terms of relative value                                   No.    (mm)         single crystal Si                                                                         polycrystalline Si                            ______________________________________                                        1      800 × 150 × 1.1                                                                3           1                                             2      700 × 150 × 1.1                                                                  2.5       1                                             3      600 × 150 × 1.1                                                                2           1                                             4      500 × 150 × 1.1                                                                  1.2       1                                             5      400 × 150 × 1.1                                                                1           1                                             6      300 × 150 × 1.1                                                                1           1                                             ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                                           mean crystal                                               Sample             grain size fitness proportion in                           No.   crystallinity                                                                              (mm)       terms of relative value                         ______________________________________                                        1     Si single crystal                                                                          --           0.4                                           2     Si polycrystalline                                                                         15           0.45                                          3     Si polycrystalline                                                                         8            0.8                                           4     Si polycrystalline                                                                         5            0.9                                           5     Si polycrystalline                                                                         2          1                                               6     Si polycrystalline                                                                         1          1                                               7     Si polycrystalline                                                                           0.1      1                                               8     Si polycrystalline                                                                           0.01     1                                               ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        Sample                  pit number  yield                                     No.     Si-base member used                                                                           (number/cm.sup.2)                                                                         (%)                                       ______________________________________                                        1       single crystal  1           95                                        2       polycrystalline silicon                                                                       1           95                                                with no addition of                                                           release agent                                                         3       polycrystalline silicon                                                                       5           95                                                with addition of                                                              release agent                                                         4       same as in sample 3                                                                           10          90                                        5       same as in sample 3                                                                           50          60                                        6       same as in sample 3                                                                           100         30                                        ______________________________________                                    

                                      TABLE 5-1                                   __________________________________________________________________________        thermally                                                                     softening                                                                            surface step state                                                                      recording head                                                                        survival rate of the                             sample                                                                            temprature                                                                           after the thermally                                                                     production                                                                            heat generating resistor                         No. (°C.)                                                                         softening treatment                                                                     possibility                                                                           1 × 10.sup.7                                                                 1 × 10.sup.8                                                                 3 × 10.sup.8                     __________________________________________________________________________    1   1380   ⊚                                                                        impossible                                                                            --   --   --                                     2   1330   ⊚                                                                        possible                                                                              100% 100% 100%                                   3   1280   ∘                                                                           possible                                                                              100% 100% 100%                                   4   1230   ∘                                                                           possible                                                                              100% 100% 100%                                   5   1180   x         possible                                                                               50%  10%  0%                                    __________________________________________________________________________

                                      TABLE 5-2                                   __________________________________________________________________________        heat  heat surface step                                                       treatment                                                                           treatment                                                                          state after                                                                         recording head                                                                        survival rate of the                             sample                                                                            temprature                                                                          period                                                                             the heat                                                                            production                                                                            heat generating resistor                         No. (°C.)                                                                        (hr) treatment                                                                           possibility                                                                           1 × 10.sup.7                                                                 1 × 10.sup.8                                                                 3 × 10.sup.8                     __________________________________________________________________________    6   1380  5    ⊚                                                                    impossible                                                                            --   --   --                                     7   1330  7    ⊚                                                                    possible                                                                              100% 100% 100%                                   8   1280  8    ∘                                                                       possible                                                                              100% 100% 100%                                   9   1230  11   ∘                                                                       possible                                                                              100% 100% 100%                                   10  1180  14   x     possible                                                                               50%  10%  0%                                    __________________________________________________________________________

                                      TABLE 5-3                                   __________________________________________________________________________               impurity-                                                                            thermally                                                                            surface step                                             diffusion                                                                            surface                                                                              softening                                                                            state after                                                                             survival rate of the                       sample                                                                            temprature                                                                           content                                                                              temperature                                                                          the thermally                                                                           heat generating resistor                   No. (°C.)                                                                         (atoms/cm.sup.3)                                                                     (°C.)                                                                         softening treatment                                                                     1 × 10.sup.7                                                                 1 × 10.sup.8                                                                 3 × 10.sup.8               __________________________________________________________________________    11  1050   5 × 10.sup.21                                                                  1280   ⊚                                                                        25%   3%  0%                               12  1050   5 × 10.sup.21                                                                  1230   ⊚                                                                        28%   5%  0%                               13  1050   5 × 10.sup.21                                                                  1180   ⊚                                                                        22%   4%  0%                               14  1050   5 × 10.sup.21                                                                  1130   ⊚                                                                        26%   3%  0%                               15  1050   5 × 10.sup.21                                                                  1080   ⊚                                                                        30%   5%  0%                               16  1000   1 × 10.sup.21                                                                  1280   ⊚                                                                        100% 100% 100%                             17  1000   1 × 10.sup.21                                                                  1230   ⊚                                                                        100% 100% 100%                             18  1000   1 × 10.sup.21                                                                  1180   ⊚                                                                        100% 100% 100%                             19  1000   1 × 10.sup.21                                                                  1130   ∘                                                                           100% 100% 100%                             20  1000   1 × 10.sup.21                                                                  1080   x         50%   10% 0%                               21   950   1 × 10.sup.20                                                                  1280   ⊚                                                                        100% 100% 100%                             22   950   1 × 10.sup.20                                                                  1230   ⊚                                                                        100% 100% 100%                             23   950   1 × 10.sup.20                                                                  1180   ∘                                                                           100% 100% 100%                             24   950   1 × 10.sup.20                                                                  1130   x         48%   11% 0%                               25   950   1 × 10.sup.20                                                                  1080   x         51%   9%  0%                               __________________________________________________________________________

                                      TABLE 6                                     __________________________________________________________________________                          surface step state                                      Sample       base member size                                                                       after the thermally                                                                     exposure fitness                              No. crystallinity                                                                          (mm)     softening treatment                                                                     proprotion                                    __________________________________________________________________________    1   Si polycrystalline                                                                     600 × 150 × 1.1                                                            ⊚                                                                        100%                                          2   Si polycrystalline                                                                     500 × 150 × 1.1                                                            ⊚                                                                        100%                                          3   Si polycrystalline                                                                     400 × 150 × 1.1                                                            ⊚                                                                        100%                                          4   Si polycrystalline                                                                     300 × 150 × 1.1                                                            ⊚                                                                        100%                                          5   Si polycrystalline                                                                     600 × 150 × 1.1                                                            ⊚                                                                        100%                                          6   Si polycrystalline                                                                     500 × 150 × 1.1                                                            ⊚                                                                        100%                                          7   Si polycrystalline                                                                     400 × 150 × 1.1                                                            ⊚                                                                        100%                                          8   Si polycrystalline                                                                     300 × 150 × 1.1                                                            ⊚                                                                        100%                                          9   Si polycrystalline                                                                     600 × 150 × 1.1                                                            ⊚                                                                        100%                                          10  Si polycrystalline                                                                     500 × 150 × 1.1                                                            ⊚                                                                        100%                                          11  Si polycrystalline                                                                     400 × 150 × 1.1                                                            ⊚                                                                        100%                                          12  Si polycrystalline                                                                     300 × 150 × 1.1                                                            ⊚                                                                        100%                                          __________________________________________________________________________

                                      TABLE 7                                     __________________________________________________________________________              base  number of                                                                           yield upon                                                                            survival rate of the                                                                         printing                                                                           printing function           Sample                                                                            crystal-                                                                            member                                                                              discharging                                                                         producing a                                                                           heat generating resistor                                                                     width                                                                              printing                                                                           appearance of          No. linity                                                                              size (mm)                                                                           outlet                                                                              recording head                                                                        1 × 10.sup.7                                                                 1 × 10.sup.8                                                                 3 × 10.sup.8                                                                 (mm) precision                                                                          uneven                 __________________________________________________________________________                                                           density                1'  Si poly-                                                                            600 ×                                                                         8576  ∘                                                                         100% 100% 100% 545  fitness                                                                            fitness                    crystalline                                                                         150 × 1.1                                                     2'  Si poly-                                                                            500 ×                                                                         7244  ∘                                                                         100% 100% 100% 460  fitness                                                                            fitness                    crystalline                                                                         150 × 1.1                                                     3'  Si poly-                                                                            400 ×                                                                         5504  ∘                                                                         100% 100% 100% 350  fitness                                                                            fitness                    crystalline                                                                         150 × 1.1                                                     4'  Si poly-                                                                            300 ×                                                                         4288  ∘                                                                         100% 100% 100% 272  fitness                                                                            fitness                    crystalline                                                                         150 × 1.1                                                     5'  Si poly-                                                                            600 ×                                                                         8576  ∘                                                                         100% 100% 100% 545  fitness                                                                            fitness                    crystalline                                                                         150 × 1.1                                                     6'  Si poly-                                                                            500 ×                                                                         7244  ∘                                                                         100% 100% 100% 460  fitness                                                                            fitness                    crystalline                                                                         150 × 1.1                                                     7'  Si poly-                                                                            400 ×                                                                         5504  ∘                                                                         100% 100% 100% 350  fitness                                                                            fitness                    crystalline                                                                         150 × 1.1                                                     8'  Si poly-                                                                            300 ×                                                                         4288  ∘                                                                         100% 100% 100% 272  fitness                                                                            fitness                    crystalline                                                                         150 × 1.1                                                     9'  Si poly-                                                                            600 ×                                                                         8576  ∘                                                                         100% 100% 100% 545  fitness                                                                            fitness                    crystalline                                                                         150 × 1.1                                                     10' Si poly-                                                                            500 ×                                                                         7244  ∘                                                                         100% 100% 100% 460  fitness                                                                            fitness                    crystalline                                                                         150 × 1.1                                                     11' Si poly-                                                                            400 ×                                                                         5504  ∘                                                                         100% 100% 100% 350  fitness                                                                            fitness                    crystalline                                                                         150 × 1.1                                                     12' Si poly-                                                                            300 ×                                                                         4288  ∘                                                                         100% 100% 100% 272  fitness                                                                            fitness                    crystalline                                                                         150 × 1.1                                                     __________________________________________________________________________

                  TABLE 8                                                         ______________________________________                                        Comparative                                                                   Sample              base member size                                                                           exposure fitness                             No.      crystallinity                                                                            (mm)         proportion                                   ______________________________________                                        1        Si single  600 × 150 × 1.1                                                                40%                                                   crystal                                                              2        Si single  500 × 150 × 1.1                                                                90%                                                   crystal                                                              3        Si single  400 × 150 × 1.1                                                                100%                                                  crystal                                                              4        Si single  300 × 150 × 1.1                                                                100%                                                  crystal                                                              ______________________________________                                    

                                      TABLE 9                                     __________________________________________________________________________              base  number of                                                                           yield upon                                                                            survival rate of the                                                                         printing                                                                           printing function           Sample                                                                            crystal-                                                                            member                                                                              discharging                                                                         producing a                                                                           heat generating resistor                                                                     width                                                                              printing                                                                           appearance of          No. linity                                                                              size (mm)                                                                           outlet                                                                              recording head                                                                        1 × 10.sup.7                                                                 1 × 10.sup.8                                                                 3 × 10.sup.8                                                                 (mm) precision                                                                          uneven                 __________________________________________________________________________                                                           density                1'  Si single                                                                           600 ×                                                                         --    x       --   --   --   --   --   --                         crystal                                                                             150 × 1.1                                                     2'  Si single                                                                           500 ×                                                                         7244  Δ 100% 100% 100% 460  fitness                                                                            fitness                    crystal                                                                             150 × 1.1                                                     3'  Si single                                                                           400 ×                                                                         5504  ∘                                                                         100% 100% 100% 350  fitness                                                                            fitness                    crystal                                                                             150 × 1.1                                                     4'  Si single                                                                           300 ×                                                                         4288  ∘                                                                         100% 100% 100% 272  fitness                                                                            fitness                    crystal                                                                             150 × 1.1                                                     __________________________________________________________________________

                                      TABLE 10                                    __________________________________________________________________________                        number of                                                                     discharging                                                                          survival rate of the   printing function           Sample     base member size                                                                       outlet heat generating resistor                                                                     printing width                                                                        printing                                                                           appearance of          No. crystallinity                                                                        (mm)     per head unit                                                                        1 × 10.sup.7                                                                 1 × 10.sup.8                                                                 3 × 10.sup.8                                                                 (mm)    precision                                                                          uneven                 __________________________________________________________________________                                                           density                4"  single crystal                                                                       (300 × 150 ×                                                               8576   100% 100% 100% 545     unfitness                                                                          unfitness                         1.1) × 2                                                     __________________________________________________________________________

I claim:
 1. A process for producing a substrate for liquid jet recordinghead provided with an electrothermal converting body comprising a heatgenerating resistor capable of generating thermal energy and a pair ofwirings electrically connected to said heat generating resistor isformed, characterized by comprising:providing a member composed of apolycrystalline material as a constituent base member of said substrate,and thermally oxidizing the surface of said polycrystalline member andthermally softening the surface of said polycrystalline member at atemperature in the range of 1230° C. to 1330° C., to thereby form athermal oxide layer on the surface of said polycrystalline member.
 2. Aprocess for producing a substrate for liquid jet recording headaccording to claim 1, wherein the polycrystalline member is apolycrystalline silicon member.
 3. A process for producing a substratefor liquid jet recording head according to claim 1, wherein thethermally oxidizing step and the thermally softening step aresuccessively conducted.
 4. A process for producing a substrate forliquid jet recording head according to claim 1, wherein the thermallyoxidizing step and the thermally softening step are concurrentlyconducted.
 5. A process for producing a substrate for liquid jetrecording head according to claim 1 which further comprises a step ofdiffusing an impurity into the polycrystalline member.
 6. A process forproducing a substrate for liquid jet recording head according to claim5, wherein the amount of the impurity incorporated into thepolycrystalline member is adjusted to be 1×10²¹ atoms/cm³ or less andthe thermally softening step is conducted at a temperature in the rangeof 1130° C. to 1330° C.
 7. A substrate for liquid jet recording headincluding an electrothermal converting body comprising a heat generatingresistor capable of generating thermal energy and a pair of wiringselectrically connected to said heat generating resistor, characterizedin that said substrate includes a base member constituted by apolycrystalline material and said polycrystalline base member has athermal oxide layer formed by subjecting the surface of saidpolycrystalline base member to thermal oxidation treatment and thermallysoftening treatment at a temperature in the range of 1230° C. to 1330°C.
 8. A substrate for liquid jet recording head according to claim 7,wherein the polycrystalline base member is a polycrystalline siliconbase member.
 9. A substrate for liquid jet recording head according toclaim 7, wherein the substrate is a substrate for full line typerecording head which has a length corresponding to the entire width ofthe recording area of a recording member on which recording isconducted.
 10. A liquid jet recording head which includes a substratefor liquid jet recording head including an electrothermal convertingbody comprising a heat generating resistor capable of generating thermalenergy and a pair of wirings electrically connected to said heatgenerating resistor, and a liquid supplying pathway disposed in thevicinity of said electrothermal converting body of said substrate,characterized in that said substrate includes a base member constitutedby a polycrystalline material and said polycrystalline base member has athermal oxide layer formed by subjecting the surface of saidpolycrystalline base member to thermal oxidation treatment and thermallysoftening treatment at a temperature in the range of 1230° C. to 1330°C.
 11. A liquid jet recording head according to claim 10, wherein thepolycrystalline member is a polycrystalline silicon base member.
 12. Aliquid jet recording head according to claim 10, wherein the substrateis a substrate for full line type recording head which has a lengthcorresponding to the entire width of the recording area of a recordingmember on which recording is conducted.
 13. A liquid jet recordingapparatus comprising: a liquid jet recording head including a substratefor liquid jet recording head including an electrothermal convertingbody comprising a heat generating resistor capable of generating thermalenergy and a pair of wirings electrically connected to said heatgenerating resistor, and a liquid supplying pathway disposed in thevicinity of said electrothermal converting body of said substratewherein said substrate includes a base member constituted by apolycrystalline material, said polycrystalline base member having athermal oxide layer formed by subjecting the surface of saidpolycrystalline base member to thermal oxidation treatment and thermallysoftening treatment at a temperature in the range of 1230° C. to 1330°C.; and an electric signal supplying means capable of supplying anelectric signal to said heat generating resistor of said recording head.14. A liquid jet recording apparatus according to claim 13, wherein thepolycrystalline member is a polycrystalline silicon base member.
 15. Aliquid jet recording apparatus according to claim 13, wherein thesubstrate is a substrate for full line type recording head which has alength corresponding to the entire width of the recording area of arecording member on which recording is conducted.
 16. A process forproducing a substrate for a liquid jet recording head provided with anelectrothermal converting body comprising a heat generating resistorcapable of generating thermal energy and a pair of wirings electricallyconnected to said heat generating resistor, comprising the stepsof:providing a member composed of a polycrystalline material as aconstituent base member of said substrate, diffusing an impurity intosaid polycrystalline member in an amount of not more than about 1×10²¹atoms/cm³, and thermally oxidizing the surface of said polycrystallinemember and thermally softening the surface of said polycrystallinemember at a temperature in the range of 1230° C. to 1330° C., to therebyform a thermal oxide layer on the surface of said polycrystallinemember.